diff --git a/TODO b/TODO
index 6c8d83b..d60252c 100644
--- a/TODO
+++ b/TODO
@@ -104,6 +104,9 @@ DARWIN
   Needs love, particularly threads and exceptions/signals. slam.sh is
   also broken there.
 
+DRAGONFLY
+  Fix multithreading support on x86-64, add it on x86.
+
 FUNCTION NAMES
 
   We'd like to be able to (SETF %FUNCTION-NAME) on a closure.
diff --git a/base-target-features.lisp-expr b/base-target-features.lisp-expr
index 74bf083..c262c1c 100644
--- a/base-target-features.lisp-expr
+++ b/base-target-features.lisp-expr
@@ -434,23 +434,24 @@
  ;;     implemented for this platform.
  ;;
  ;; operating system features:
- ;;   :unix    = We're intended to run under some Unix-like OS. (This is not
- ;;              exclusive with the features which indicate which particular
- ;;              Unix-like OS we're intended to run under.)
- ;;   :linux   = We're intended to run under some version of Linux.
- ;;   :bsd     = We're intended to run under some version of BSD Unix. (This
- ;;              is not exclusive with the features which indicate which
- ;;              particular version of BSD we're intended to run under.)
- ;;   :freebsd = We're intended to run under FreeBSD.
- ;;   :openbsd = We're intended to run under OpenBSD.
- ;;   :netbsd  = We're intended to run under NetBSD.
- ;;   :darwin  = We're intended to run under Darwin (including MacOS X).
- ;;   :sunos   = We're intended to run under Solaris user environment
- ;;              with the SunOS kernel.
- ;;   :hpux    = We're intended to run under HP-UX 11.11 or later
- ;;   :osf1    = We're intended to run under Tru64 (aka Digital Unix
- ;;              aka OSF/1).
- ;;   :win32   = We're intended to under some version of Microsoft Windows.
+ ;;   :unix       = We're intended to run under some Unix-like OS. (This is not
+ ;;                 exclusive with the features which indicate which particular
+ ;;                 Unix-like OS we're intended to run under.)
+ ;;   :linux      = We're intended to run under some version of Linux.
+ ;;   :bsd        = We're intended to run under some version of BSD Unix. (This
+ ;;                 is not exclusive with the features which indicate which
+ ;;                 particular version of BSD we're intended to run under.)
+ ;;   :freebsd    = We're intended to run under FreeBSD.
+ ;;   :openbsd    = We're intended to run under OpenBSD.
+ ;;   :netbsd     = We're intended to run under NetBSD.
+ ;;   :dragonfly  = We're intended to run under DragonFly.
+ ;;   :darwin     = We're intended to run under Darwin (including MacOS X).
+ ;;   :sunos      = We're intended to run under Solaris user environment
+ ;;                 with the SunOS kernel.
+ ;;   :hpux       = We're intended to run under HP-UX 11.11 or later
+ ;;   :osf1       = We're intended to run under Tru64 (aka Digital Unix
+ ;;                 aka OSF/1).
+ ;;   :win32      = We're intended to under some version of Microsoft Windows.
  ;; (No others are supported by SBCL as of 1.0.8, but :hpux or :irix
  ;; support could be ported from CMU CL if anyone is sufficiently
  ;; motivated to do so.)
diff --git a/contrib/asdf/asdf.lisp b/contrib/asdf/asdf.lisp
index ce7a1db..6274595 100644
--- a/contrib/asdf/asdf.lisp
+++ b/contrib/asdf/asdf.lisp
@@ -3237,7 +3237,7 @@ located."
    '(:cygwin (:win :windows :mswindows :win32 :mingw32) ;; try cygwin first!
      (:linux :linux :linux-target) ;; for GCL at least, must appear before :bsd
      (:macosx :macosx :darwin :darwin-target :apple) ; also before :bsd
-     (:solaris :solaris :sunos) (:bsd :bsd :freebsd :netbsd :openbsd) :unix
+     (:solaris :solaris :sunos) (:bsd :bsd :freebsd :dragonfly :netbsd :openbsd) :unix
      :genera)))
 
 (defun architecture ()
diff --git a/contrib/sb-bsd-sockets/constants.lisp b/contrib/sb-bsd-sockets/constants.lisp
index eeabd11..b874b17 100644
--- a/contrib/sb-bsd-sockets/constants.lisp
+++ b/contrib/sb-bsd-sockets/constants.lisp
@@ -316,7 +316,7 @@
  (:integer EAI-BADFLAGS "EAI_BADFLAGS")
  (:integer EAI-NONAME "EAI_NONAME")
  (:integer EAI-SERVICE "EAI_SERVICE")
- #-freebsd
+ #-(or freebsd dragonfly)
  (:integer EAI-ADDRFAMILY "EAI_ADDRFAMILY")
  (:integer EAI-MEMORY "EAI_MEMORY")
  (:integer EAI-FAIL "EAI_FAIL")
diff --git a/contrib/sb-bsd-sockets/tests.lisp b/contrib/sb-bsd-sockets/tests.lisp
index 776878c..f9e8c1b 100644
--- a/contrib/sb-bsd-sockets/tests.lisp
+++ b/contrib/sb-bsd-sockets/tests.lisp
@@ -30,6 +30,7 @@
 ;;; Apparently getprotobyname_r on FreeBSD says -1 and EINTR
 ;;; for unknown protocols...
 #-(and freebsd sb-thread)
+#-(and dragonfly sb-thread)
 (deftest get-protocol-by-name/error
   (handler-case (get-protocol-by-name "nonexistent-protocol")
     (unknown-protocol ()
diff --git a/make-config.sh b/make-config.sh
index 6b720e0..04a2dda 100644
--- a/make-config.sh
+++ b/make-config.sh
@@ -277,6 +277,9 @@ case `uname` in
                 ;;
         esac
         ;;
+    DragonFly)
+	sbcl_os="dragonfly"
+	;;
     Darwin)
         sbcl_os="darwin"
         ;;
@@ -385,7 +388,8 @@ then
     # If --fancy, enable threads on platforms where they can be built.
     case $sbcl_arch in
         x86|x86-64|ppc)
-	    if [ "$sbcl_os" = "sunos" ] && [ "$sbcl_arch" = "x86-64" ]
+	    if ([ "$sbcl_os" = "sunos" ] && [ "$sbcl_arch" = "x86-64" ]) || \
+               ([ "$sbcl_os" = "dragonfly" ] && [ "$sbcl_arch" = "x86" ])
 	    then
 		echo "No threads on this platform."
 	    else
@@ -502,6 +506,16 @@ case "$sbcl_os" in
                 ;;
         esac
         ;;
+    dragonfly)
+        printf ' :unix' >> $ltf
+        printf ' :bsd' >> $ltf
+        printf ' :elf' >> $ltf
+        printf ' :dragonfly' >> $ltf
+        printf ' :sb-qshow' >> $ltf
+        link_or_copy $sbcl_arch-bsd-os.h target-arch-os.h
+        link_or_copy bsd-os.h target-os.h
+        link_or_copy Config.$sbcl_arch-dragonfly Config
+        ;;
     darwin)
         printf ' :unix' >> $ltf
         printf ' :mach-o' >> $ltf
@@ -587,7 +601,7 @@ if [ "$sbcl_arch" = "x86" ]; then
     printf ' :alien-callbacks :cycle-counter :inline-constants ' >> $ltf
     printf ' :memory-barrier-vops :multiply-high-vops' >> $ltf
     case "$sbcl_os" in
-    linux | freebsd | netbsd | openbsd | sunos | darwin | win32)
+    linux | freebsd | netbsd | openbsd | sunos | darwin | win32 | dragonfly)
         printf ' :linkage-table' >> $ltf
     esac
     if [ "$sbcl_os" = "win32" ]; then
diff --git a/src/code/unix.lisp b/src/code/unix.lisp
index 9572a22..de330ae 100644
--- a/src/code/unix.lisp
+++ b/src/code/unix.lisp
@@ -414,14 +414,14 @@ corresponds to NAME, or NIL if there is none."
   ;; comma not inside a backquote. This error has absolutely nothing
   ;; to do with the actual meaning of the error (and little to do with
   ;; its location, either).
-  #!-(or linux openbsd freebsd netbsd sunos osf1 darwin hpux win32) (,stub,)
-  #!+(or linux openbsd freebsd netbsd sunos osf1 darwin hpux win32)
+  #!-(or linux openbsd freebsd netbsd sunos osf1 darwin hpux win32 dragonfly) (,stub,)
+  #!+(or linux openbsd freebsd netbsd sunos osf1 darwin hpux win32 dragonfly)
   (or (newcharstar-string (alien-funcall (extern-alien "getcwd"
                                                        (function (* char)
                                                                  (* char)
                                                                  size-t))
                                          nil
-                                         #!+(or linux openbsd freebsd netbsd darwin win32) 0
+                                         #!+(or linux openbsd freebsd netbsd dragonfly darwin win32) 0
                                          #!+(or sunos osf1 hpux) 1025))
       (simple-perror "getcwd")))
 
diff --git a/src/compiler/x86/parms.lisp b/src/compiler/x86/parms.lisp
index 5502afd..163ffd7 100644
--- a/src/compiler/x86/parms.lisp
+++ b/src/compiler/x86/parms.lisp
@@ -187,13 +187,14 @@
 ;;; NetBSD configuration used to have this comment regarding the linkage
 ;;; table: "In CMUCL: 0xB0000000->0xB1000000"
 
-#!+win32   (!gencgc-space-setup #x22000000 nil nil #x10000)
-#!+linux   (!gencgc-space-setup #x01000000 #x09000000)
-#!+sunos   (!gencgc-space-setup #x20000000 #x48000000)
-#!+freebsd (!gencgc-space-setup #x01000000 #x58000000)
-#!+openbsd (!gencgc-space-setup #x1b000000 #x40000000)
-#!+netbsd  (!gencgc-space-setup #x20000000 #x60000000)
-#!+darwin  (!gencgc-space-setup #x04000000 #x10000000)
+#!+win32     (!gencgc-space-setup #x22000000 nil nil #x10000)
+#!+linux     (!gencgc-space-setup #x01000000 #x09000000)
+#!+sunos     (!gencgc-space-setup #x20000000 #x48000000)
+#!+freebsd   (!gencgc-space-setup #x01000000 #x58000000)
+#!+dragonfly (!gencgc-space-setup #x01000000 #x58000000)
+#!+openbsd   (!gencgc-space-setup #x1b000000 #x40000000)
+#!+netbsd    (!gencgc-space-setup #x20000000 #x60000000)
+#!+darwin    (!gencgc-space-setup #x04000000 #x10000000)
 
 ;;; Size of one linkage-table entry in bytes.
 (def!constant linkage-table-entry-size 8)
diff --git a/src/runtime/Config.x86-64-dragonfly b/src/runtime/Config.x86-64-dragonfly
new file mode 100644
index 0000000..f00b739
--- /dev/null
+++ b/src/runtime/Config.x86-64-dragonfly
@@ -0,0 +1,26 @@
+# -*- makefile -*- for the C-level run-time support for SBCL
+
+# This software is part of the SBCL system. See the README file for
+# more information.
+#
+# This software is derived from the CMU CL system, which was
+# written at Carnegie Mellon University and released into the
+# public domain. The software is in the public domain and is
+# provided with absolutely no warranty. See the COPYING and CREDITS
+# files for more information.
+
+include Config.x86-64-bsd
+
+ASSEM_SRC += ldso-stubs.S
+
+# Until sbcl-0.6.7.3, we used "LINKFLAGS+=-static" here, which
+# worked fine for most things, but LOAD-FOREIGN & friends require
+# dlopen() etc., which in turn depend on dynamic linking of the
+# runtime.
+LINKFLAGS += -dynamic -export-dynamic
+
+# use 1:1 threading.
+# FIXME: DragonFly's lpthread must be what we need.
+ifdef LISP_FEATURE_SB_THREAD
+  OS_LIBS += -lpthread
+endif
diff --git a/src/runtime/Config.x86-dragonfly b/src/runtime/Config.x86-dragonfly
new file mode 100644
index 0000000..ab834fb
--- /dev/null
+++ b/src/runtime/Config.x86-dragonfly
@@ -0,0 +1,26 @@
+# -*- makefile -*- for the C-level run-time support for SBCL
+
+# This software is part of the SBCL system. See the README file for
+# more information.
+#
+# This software is derived from the CMU CL system, which was
+# written at Carnegie Mellon University and released into the
+# public domain. The software is in the public domain and is
+# provided with absolutely no warranty. See the COPYING and CREDITS
+# files for more information.
+
+include Config.x86-bsd
+
+ASSEM_SRC += ldso-stubs.S
+
+# Until sbcl-0.6.7.3, we used "LINKFLAGS+=-static" here, which
+# worked fine for most things, but LOAD-FOREIGN & friends require
+# dlopen() etc., which in turn depend on dynamic linking of the
+# runtime.
+LINKFLAGS += -dynamic -export-dynamic
+
+ifdef LISP_FEATURE_SB_THREAD
+  OS_LIBS += -lpthread
+endif
+
+CFLAGS += -fno-omit-frame-pointer
diff --git a/src/runtime/bsd-os.c b/src/runtime/bsd-os.c
index 4c08b97..d308d9b 100644
--- a/src/runtime/bsd-os.c
+++ b/src/runtime/bsd-os.c
@@ -72,6 +72,12 @@ static void netbsd_init();
 static void freebsd_init();
 #endif /* __FreeBSD__ */
 
+#ifdef __DragonFly__
+#include <sys/sysctl.h>
+
+static void dragonfly_init();
+#endif /* __DragonFly__ */
+
 #ifdef __OpenBSD__
 #include <sys/types.h>
 #include <sys/resource.h>
@@ -98,6 +104,8 @@ os_init(char *argv[], char *envp[])
     openbsd_init();
 #elif defined(LISP_FEATURE_DARWIN)
     darwin_init();
+#elif defined(__DragonFly__)
+    dragonfly_init();
 #endif
 }
 
@@ -107,7 +115,7 @@ os_context_sigmask_addr(os_context_t *context)
     /* (Unlike most of the other context fields that we access, the
      * signal mask field is a field of the basic, outermost context
      * struct itself both in FreeBSD 4.0 and in OpenBSD 2.6.) */
-#if defined(__FreeBSD__)  || defined(__NetBSD__) || defined(LISP_FEATURE_DARWIN)
+#if defined(__FreeBSD__)  || defined(__NetBSD__) || defined(LISP_FEATURE_DARWIN) || defined(__DragonFly__)
     return &context->uc_sigmask;
 #elif defined (__OpenBSD__)
     return &context->sc_mask;
@@ -444,6 +452,58 @@ futex_wake(int *lock_word, int n)
 #endif
 #endif /* __FreeBSD__ */
 
+#ifdef __DragonFly__
+static void dragonfly_init()
+{
+#ifdef LISP_FEATURE_X86
+    size_t len;
+    int instruction_sse;
+    
+    len = sizeof(instruction_sse);
+    if (sysctlbyname("hw.instruction_sse", &instruction_sse, &len,
+                     NULL, 0) == 0 && instruction_sse != 0) {
+        /* Use the SSE detector */
+        fast_bzero_pointer = fast_bzero_detect;
+    }
+#endif /* LISP_FEATURE_X86 */
+}
+
+
+#if defined(LISP_FEATURE_SB_THREAD) && defined(LISP_FEATURE_SB_FUTEX) \
+    && !defined(LISP_FEATURE_SB_PTHREAD_FUTEX)
+int
+futex_wait(int *lock_word, long oldval, long sec, unsigned long usec)
+{
+    int ret;
+
+    if (sec < 0)
+        ret = umtx_sleep(lock_word, oldval, 0);
+    else {
+        int count = usec + 1000000 * sec;
+        ret = umtx_sleep(lock_word, oldval, count);
+    }
+
+    if (ret == 0) return 0;
+    else {
+        switch (errno) {
+        case EWOULDBLOCK: // Operation timed out
+            return 1;
+        case EINTR:
+            return 2;
+        default: // Such as EINVAL or EBUSY
+            return -1;
+        }
+    }
+}
+
+int
+futex_wake(int *lock_word, int n)
+{
+    return umtx_wakeup(lock_word, n);
+}
+#endif
+#endif /* __DragonFly__ */
+
 #ifdef LISP_FEATURE_DARWIN
 /* defined in ppc-darwin-os.c instead */
 #elif defined(LISP_FEATURE_FREEBSD)
@@ -478,6 +538,20 @@ os_get_runtime_executable_path(int external)
         return NULL;
     return copied_string(path);
 }
+#elif defined(LISP_FEATURE_DRAGONFLY)
+char *
+os_get_runtime_executable_path(int external)
+{
+    char path[PATH_MAX + 1];
+    int size = readlink("/proc/curproc/file", path, sizeof(path) - 1);
+    if (size < 0)
+        return NULL;
+    path[size] = '\0';
+
+    if (strcmp(path, "unknown") == 0)
+        return NULL;
+    return copied_string(path);
+}
 #elif defined(LISP_FEATURE_NETBSD) || defined(LISP_FEATURE_OPENBSD)
 char *
 os_get_runtime_executable_path(int external)
@@ -487,7 +561,7 @@ os_get_runtime_executable_path(int external)
         return copied_string("/proc/curproc/file");
     return NULL;
 }
-#else /* Not DARWIN or FREEBSD or NETBSD or OPENBSD */
+#else /* Not DARWIN or FREEBSD or NETBSD or OPENBSD or DragonFly */
 char *
 os_get_runtime_executable_path(int external)
 {
diff --git a/src/runtime/bsd-os.h b/src/runtime/bsd-os.h
index 880c5f7..61aaf0e 100644
--- a/src/runtime/bsd-os.h
+++ b/src/runtime/bsd-os.h
@@ -9,7 +9,7 @@
  * files for more information.
  */
 
-#ifdef __FreeBSD__
+#if defined(__FreeBSD__) || defined(__DragonFly__)
 #include <osreldate.h>
 #endif
 
@@ -61,6 +61,14 @@ extern int sig_memory_fault;
 
 #define SIG_STOP_FOR_GC (SIGUSR2)
 
+#elif defined __DragonFly__
+
+#include <sys/ucontext.h>
+typedef ucontext_t os_context_t;
+
+#define SIG_MEMORY_FAULT (SIGSEGV)
+#define SIG_STOP_FOR_GC (SIGUSR2)
+
 #elif defined __OpenBSD__
 
 typedef struct sigcontext os_context_t;
diff --git a/src/runtime/pthread-futex.c b/src/runtime/pthread-futex.c
index cddcda9..209480c 100644
--- a/src/runtime/pthread-futex.c
+++ b/src/runtime/pthread-futex.c
@@ -279,7 +279,7 @@ again:
          * emulate this behaviour. */
         sigpending(&pendset);
         for (i = 1; i < NSIG; i++) {
-            if (sigismember(&pendset, i) && sigismember(&newset, i)) {
+            if (sigismember(&pendset, i) && sigismember(&oldset, i)) {
                 result = EINTR;
                 goto done;
             }
diff --git a/src/runtime/thread.c b/src/runtime/thread.c
index 26f6de6..dd89435 100644
--- a/src/runtime/thread.c
+++ b/src/runtime/thread.c
@@ -58,7 +58,7 @@
 #define LOCK_CREATE_THREAD
 #endif
 
-#ifdef LISP_FEATURE_FREEBSD
+#if defined(LISP_FEATURE_FREEBSD) || defined(LISP_FEATURE_DRAGONFLY)
 #define CREATE_CLEANUP_THREAD
 #define LOCK_CREATE_THREAD
 #endif
diff --git a/src/runtime/undefineds.h b/src/runtime/undefineds.h
index b1cb325..024b565 100644
--- a/src/runtime/undefineds.h
+++ b/src/runtime/undefineds.h
@@ -39,7 +39,8 @@ F(brk)
      || defined(SVR4) \
      || defined(__FreeBSD__) \
      || defined(__OpenBSD__) \
-     || defined(__NetBSD__)
+     || defined(__NetBSD__) \
+     || defined(__DragonFly__)
 F(cfgetospeed)
 F(cfsetospeed)
 F(cfgetispeed)
@@ -154,7 +155,7 @@ F(sigreturn)
 #if !defined(SVR4)
 F(sigsetmask)
 #endif
-#if !defined(SVR4) && !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__)
+#if !defined(SVR4) && !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__) && !defined(__DragonFly__)
 F(sigstack)
 F(sigvec)
 #endif
@@ -180,6 +181,7 @@ F(readdir)
      || defined(__FreeBSD__) \
      || defined(__OpenBSD__) \
      || defined(__NetBSD__) \
+     || defined(__DragonFly__) \
      || defined(__linux__)
 F(tcgetattr)
 F(tcsetattr)
@@ -198,6 +200,7 @@ F(umask)
      && !defined(SOLARIS) \
      && !defined(__OpenBSD__) \
      && !defined(__FreeBSD__) \
+     && !defined(__DragonFly__) \
      && !defined(__NetBSD__)
 F(umount)
 #endif
@@ -208,7 +211,7 @@ F(utimes)
 #ifndef irix
 F(vfork)
 #endif
-#if !defined(osf1) && !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__)
+#if !defined(osf1) && !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__) && !defined(__DragonFly__)
 F(vhangup)
 #endif
 F(wait)
diff --git a/src/runtime/x86-64-arch.c b/src/runtime/x86-64-arch.c
index 2e6ea23..f0831cf 100644
--- a/src/runtime/x86-64-arch.c
+++ b/src/runtime/x86-64-arch.c
@@ -70,7 +70,7 @@ context_eflags_addr(os_context_t *context)
      * we need to do this nasty absolute index magic number thing
      * instead. */
     return &context->uc_mcontext.gregs[17];
-#elif defined __FreeBSD__
+#elif defined(__FreeBSD__) || defined(__DragonFly__)
     return &context->uc_mcontext.mc_rflags;
 #elif defined LISP_FEATURE_DARWIN
     return CONTEXT_ADDR_FROM_STEM(rflags);
diff --git a/src/runtime/x86-64-assem.S b/src/runtime/x86-64-assem.S
index b85639e..61924a5 100644
--- a/src/runtime/x86-64-assem.S
+++ b/src/runtime/x86-64-assem.S
@@ -25,7 +25,7 @@
 #include "genesis/thread.h"
 	
 /* Minimize conditionalization for different OS naming schemes. */
-#if defined __linux__  || defined __FreeBSD__ || defined __OpenBSD__ || defined __NetBSD__ || defined __sun || defined _WIN64
+#if defined __linux__  || defined __FreeBSD__ || defined __OpenBSD__ || defined __NetBSD__ || defined __sun || defined _WIN64 || defined __DragonFly__
 #define GNAME(var) var
 #else
 #define GNAME(var) _##var
@@ -33,7 +33,7 @@
 
 /* Get the right type of alignment. Linux, FreeBSD and OpenBSD
  * want alignment in bytes. */
-#if defined(__linux__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined __NetBSD__ || defined(__sun) || defined _WIN64
+#if defined(__linux__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined __NetBSD__ || defined(__sun) || defined _WIN64 || defined(__DragonFly__)
 #define align_4byte	4
 #define align_8byte	8
 #define align_16byte	16
diff --git a/src/runtime/x86-64-bsd-os.c b/src/runtime/x86-64-bsd-os.c
index 3d9a9c7..b394118 100644
--- a/src/runtime/x86-64-bsd-os.c
+++ b/src/runtime/x86-64-bsd-os.c
@@ -12,6 +12,10 @@
 #include <machine/fpu.h>
 #endif
 
+#if defined(LISP_FEATURE_DRAGONFLY)
+#include <machine/npx.h>
+#endif
+
 /* KLUDGE: There is strong family resemblance in the signal context
  * stuff in FreeBSD and OpenBSD, but in detail they're different in
  * almost every line of code. It would be nice to find some way to
@@ -23,7 +27,7 @@
  * entails; unfortunately, currently the situation is worse, not
  * better, than in the above paragraph. */
 
-#if defined(LISP_FEATURE_FREEBSD) || defined(LISP_FEATURE_DARWIN) || defined(LISP_FEATURE_OPENBSD)
+#if defined(LISP_FEATURE_FREEBSD) || defined(LISP_FEATURE_DARWIN) || defined(LISP_FEATURE_OPENBSD) || defined(LISP_FEATURE_DRAGONFLY)
 os_context_register_t *
 os_context_register_addr(os_context_t *context, int offset)
 {
@@ -168,6 +172,19 @@ int arch_os_thread_cleanup(struct thread *thread) {
     return 1;                  /* success */
 }
 
+#if defined(LISP_FEATURE_DRAGONFLY)
+void
+os_restore_fp_control(os_context_t *context)
+{
+    struct envxmm *ex = (struct envxmm*)(&context->uc_mcontext.mc_fpregs);
+    /* reset exception flags and restore control flags on SSE2 FPU */
+    unsigned int temp = (ex->en_mxcsr) & ~0x3F;
+    asm ("ldmxcsr %0" : : "m" (temp));
+    /* same for x87 FPU. */
+    asm ("fldcw %0" : : "m" (ex->en_cw));
+}
+#endif
+
 #if defined(LISP_FEATURE_FREEBSD)
 void
 os_restore_fp_control(os_context_t *context)
diff --git a/src/runtime/x86-64-bsd-os.h b/src/runtime/x86-64-bsd-os.h
index 9db3ae7..789748b 100644
--- a/src/runtime/x86-64-bsd-os.h
+++ b/src/runtime/x86-64-bsd-os.h
@@ -5,6 +5,10 @@
 #include <machine/fpu.h>
 #endif
 
+#ifdef LISP_FEATURE_DRAGONFLY
+#include <machine/npx.h>
+#endif
+
 typedef register_t os_context_register_t;
 
 static inline os_context_t *arch_os_get_context(void **void_context)
@@ -16,7 +20,7 @@ static inline os_context_t *arch_os_get_context(void **void_context)
  * store signal context information, but at least they tend to use the
  * same stems to name the structure fields, so by using this macro we
  * can share a fair amount of code between different variants. */
-#if defined __FreeBSD__
+#if defined(__FreeBSD__) || defined(__DragonFly__)
 #define CONTEXT_ADDR_FROM_STEM(stem) &context->uc_mcontext.mc_ ## stem
 #elif defined(__OpenBSD__)
 #define CONTEXT_ADDR_FROM_STEM(stem) &context->sc_ ## stem
@@ -26,6 +30,20 @@ static inline os_context_t *arch_os_get_context(void **void_context)
 #error unsupported BSD variant
 #endif
 
+#if defined LISP_FEATURE_DRAGONFLY
+#define RESTORE_FP_CONTROL_FROM_CONTEXT
+void os_restore_fp_control(os_context_t *context);
+
+#define X86_64_SIGFPE_FIXUP
+
+static inline unsigned int *
+arch_os_context_mxcsr_addr(os_context_t *context)
+{
+    struct envxmm *ex = (struct envxmm *)(&context->uc_mcontext.mc_fpregs);
+    return &ex->en_mxcsr;
+}
+#endif
+
 #if defined LISP_FEATURE_FREEBSD
 #define RESTORE_FP_CONTROL_FROM_CONTEXT
 void os_restore_fp_control(os_context_t *context);
diff --git a/src/runtime/x86-arch.c b/src/runtime/x86-arch.c
index dfbf908..59ecf92 100644
--- a/src/runtime/x86-arch.c
+++ b/src/runtime/x86-arch.c
@@ -68,7 +68,7 @@ context_eflags_addr(os_context_t *context)
      * we need to do this nasty absolute index magic number thing
      * instead. */
     return &context->uc_mcontext.gregs[16];
-#elif defined __FreeBSD__
+#elif defined(__FreeBSD__) || defined(__DragonFly__)
     return &context->uc_mcontext.mc_eflags;
 #elif defined __OpenBSD__
     return &context->sc_eflags;
diff --git a/src/runtime/x86-assem.S b/src/runtime/x86-assem.S
index fba970b..024e137 100644
--- a/src/runtime/x86-assem.S
+++ b/src/runtime/x86-assem.S
@@ -32,7 +32,7 @@
  *
  * (Except Win32, which is unlikely ever to be ELF, sorry. -- AB 2005-12-08)
  */
-#if defined __linux__  || defined __FreeBSD__ || defined __NetBSD__ || defined __OpenBSD__ || defined __sun
+#if defined __linux__  || defined __FreeBSD__ || defined __NetBSD__ || defined __OpenBSD__ || defined __sun || defined __DragonFly__
 #define GNAME(var) var
 #else
 #define GNAME(var) _##var
@@ -47,7 +47,7 @@
  * matter any more, perhaps it's just clutter we could get
  * rid of? -- WHN 2004-04-18)
  */
-#if defined(__linux__) || defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__sun) || defined(LISP_FEATURE_WIN32)
+#if defined(__linux__) || defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__sun) || defined(LISP_FEATURE_WIN32) || defined(__Dragonfly__)
 #define align_4byte	4
 #define align_8byte	8
 #define align_16byte	16
@@ -131,7 +131,7 @@
 # define LoadCurrentThreadSlot(offset,reg);     \
 	movl	SBCL_THREAD_BASE_EA, reg ;      \
 	movl	offset(reg), reg ;
-#elif defined(LISP_FEATURE_LINUX) || defined(LISP_FEATURE_SUNOS) || defined(LISP_FEATURE_FREEBSD)
+#elif defined(LISP_FEATURE_LINUX) || defined(LISP_FEATURE_SUNOS) || defined(LISP_FEATURE_FREEBSD) || defined(LISP_FEATURE_DRAGONFLY)
   /* see comment in arch_os_thread_init */
 # define SBCL_THREAD_BASE_EA %fs:THREAD_SELFPTR_OFFSET
 # define MAYBE_FS(addr) addr
diff --git a/src/runtime/x86-bsd-os.c b/src/runtime/x86-bsd-os.c
index fe75566..4f985fe 100644
--- a/src/runtime/x86-bsd-os.c
+++ b/src/runtime/x86-bsd-os.c
@@ -16,7 +16,7 @@
 #endif /* LISP_FEATURE_DARWIN */
 #endif
 
-#if defined(LISP_FEATURE_FREEBSD)
+#if defined(LISP_FEATURE_FREEBSD) || defined(LISP_FEATURE_DRAGONFLY)
 #include "machine/npx.h"
 #endif
 
@@ -40,7 +40,7 @@
  * entails; unfortunately, currently the situation is worse, not
  * better, than in the above paragraph. */
 
-#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(LISP_FEATURE_DARWIN)
+#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(LISP_FEATURE_DARWIN) || defined(__DragonFly__)
 int *
 os_context_register_addr(os_context_t *context, int offset)
 {
@@ -72,7 +72,7 @@ os_context_sp_addr(os_context_t *context)
     return (int *)CONTEXT_ADDR_FROM_STEM(esp);
 }
 
-#endif /* __FreeBSD__ || __OpenBSD__ */
+#endif /* __FreeBSD__ || __OpenBSD__ || __DragonFly__ */
 
 #ifdef __NetBSD__
 int *
@@ -112,7 +112,7 @@ os_context_sp_addr(os_context_t *context)
 
 int *os_context_pc_addr(os_context_t *context)
 {
-#if defined __FreeBSD__
+#if defined(__FreeBSD__) || defined(__DragonFly__)
     return CONTEXT_ADDR_FROM_STEM(eip);
 #elif defined __OpenBSD__
     return CONTEXT_ADDR_FROM_STEM(pc);
@@ -264,6 +264,14 @@ os_restore_fp_control(os_context_t *context)
 }
 #endif
 
+#if defined(LISP_FEATURE_DRAGONFLY)
+void os_restore_fp_control (os_context_t *context)
+{
+    struct envxmm *ex = (struct envxmm *)(context->uc_mcontext.mc_fpregs);
+    __asm__ __volatile__ ("fldcw %0" : : "m" (ex->en_cw));
+}
+#endif /* LISP_FEATURE_DRAGONFLY */
+
 #if defined(LISP_FEATURE_OPENBSD)
 void
 os_restore_fp_control(os_context_t *context)
diff --git a/src/runtime/x86-bsd-os.h b/src/runtime/x86-bsd-os.h
index dc9d9f7..2ae7d61 100644
--- a/src/runtime/x86-bsd-os.h
+++ b/src/runtime/x86-bsd-os.h
@@ -1,7 +1,7 @@
 #ifndef _X86_BSD_OS_H
 #define _X86_BSD_OS_H
 
-#ifdef LISP_FEATURE_FREEBSD
+#if defined(LISP_FEATURE_FREEBSD) || defined(LISP_FEATURE_DRAGONFLY)
 #include <machine/segments.h>
 #include <machine/cpufunc.h>
 #endif
@@ -17,7 +17,7 @@ static inline os_context_t *arch_os_get_context(void **void_context)
  * store signal context information, but at least they tend to use the
  * same stems to name the structure fields, so by using this macro we
  * can share a fair amount of code between different variants. */
-#if defined __FreeBSD__
+#if defined(__FreeBSD__) || defined(__DragonFly__)
 #define CONTEXT_ADDR_FROM_STEM(stem) &context->uc_mcontext.mc_ ## stem
 #elif defined(__OpenBSD__)
 #define CONTEXT_ADDR_FROM_STEM(stem) &context->sc_ ## stem
@@ -35,7 +35,7 @@ void os_restore_tls_segment_register(os_context_t *context);
 void os_restore_fp_control(os_context_t *context);
 #endif
 
-#if defined LISP_FEATURE_OPENBSD
+#if defined(LISP_FEATURE_OPENBSD) || defined(LISP_FEATURE_DRAGONFLY)
 #define RESTORE_FP_CONTROL_FROM_CONTEXT
 void os_restore_fp_control(os_context_t *context);
 #endif