Index: src/create.c
===================================================================
--- src/create.c	2017-12-17 11:14:40.000000000 +0100
+++ src/create.c	2018-04-20 07:18:23.407789197 +0200
@@ -556,8 +556,9 @@
       GNAME_TO_CHARS (gname, header->header.gname);
     }
 
-  strcpy (header->buffer + offsetof (struct posix_header, magic),
-	  OLDGNU_MAGIC);
+  strncpy (header->header.magic, OLDGNU_MAGIC, sizeof(header->header.magic));
+  strncpy (header->header.version, OLDGNU_MAGIC+sizeof(header->header.magic),
+           sizeof(header->header.version));
   header->header.typeflag = type;
   finish_header (st, header, -1);
 
@@ -909,10 +910,11 @@
       break;
 
     case OLDGNU_FORMAT:
-    case GNU_FORMAT:   /*FIXME?*/
-      /* Overwrite header->header.magic and header.version in one blow.  */
-      strcpy (header->buffer + offsetof (struct posix_header, magic),
-	      OLDGNU_MAGIC);
+    case GNU_FORMAT:
+      /* OLDGNU_MAGIC is string with 7 chars + NULL */
+      strncpy (header->header.magic, OLDGNU_MAGIC, sizeof(header->header.magic));
+      strncpy (header->header.version, OLDGNU_MAGIC+sizeof(header->header.magic),
+               sizeof(header->header.version));
       break;
 
     case POSIX_FORMAT: