Index: sd-as3525.c
===================================================================
--- sd-as3525.c	(revision 27074)
+++ sd-as3525.c	(working copy)
@@ -788,6 +786,27 @@
             goto sd_transfer_error;
         }
 
+        static int cur_bus_width = 1;
+        int new_bus_width;
+
+        if (write)
+            new_bus_width = 1; /* 4bit causes write errors somehow, switch back to 1bit for writes */
+        else
+            new_bus_width = 4;
+
+        if (cur_bus_width != new_bus_width) {
+            unsigned long response;
+            cur_bus_width = new_bus_width;
+            /* ACMD6  */
+            if(!send_cmd(drive, SD_SET_BUS_WIDTH, new_bus_width == 1 ? 0 : 2, MCI_ARG|MCI_RESP, &response))
+                goto sd_transfer_error;
+            /* Update controller setting */
+            if (new_bus_width == 1)
+                MCI_CLOCK(drive) &= ~MCI_CLOCK_WIDEBUS;
+            else
+                MCI_CLOCK(drive) |= MCI_CLOCK_WIDEBUS;
+        }
+
         if(!send_cmd(drive, cmd, bank_start, MCI_ARG, NULL))
         {
             ret -= 3*20;