diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index 4f6761d..810ae4c 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -2631,6 +2631,18 @@ merge_decls (tree newdecl, tree olddecl, tree newtype, tree oldtype)
   else if (DECL_PRESERVE_P (newdecl))
     DECL_PRESERVE_P (olddecl) = 1;

+  int decl_common = 0;
+  /* check for 'common' attribute (PR49551) */
+  if (TREE_CODE (olddecl) == VAR_DECL
+      && TREE_CODE (newdecl) == VAR_DECL)
+    {
+      if (lookup_attribute ("common", DECL_ATTRIBUTES (newdecl))
+        || lookup_attribute ("nocommon", DECL_ATTRIBUTES (newdecl)))
+       decl_common = DECL_COMMON (newdecl);
+      else
+       decl_common = DECL_COMMON (olddecl) && DECL_COMMON (newdecl);
+    }
+
   /* Copy most of the decl-specific fields of NEWDECL into OLDDECL.
      But preserve OLDDECL's DECL_UID, DECL_CONTEXT and
      DECL_ARGUMENTS (if appropriate).  */
@@ -2694,6 +2706,8 @@ merge_decls (tree newdecl, tree olddecl, tree newtype, tree oldtype)
     DECL_CONTEXT (olddecl) = olddecl_context;
     if (TREE_CODE (olddecl) == FUNCTION_DECL)
       DECL_ARGUMENTS (olddecl) = olddecl_arguments;
+    if (TREE_CODE (olddecl) == VAR_DECL)
+      DECL_COMMON (olddecl) = decl_common;
   }

   /* If OLDDECL had its DECL_RTL instantiated, re-invoke make_decl_rtl