diff --git a/libgfortran/ChangeLog b/libgfortran/ChangeLog
index c18391f106f..fcbc5483472 100644
--- a/libgfortran/ChangeLog
+++ b/libgfortran/ChangeLog
@@ -1,3 +1,9 @@
+2013-11-18  Francois-Xavier Coudert  <fxcoudert@gcc.gnu.org>
+
+	PR libfortran/51828
+	* intrinsics/unpack_generic.c (unpack_internal): Let the compiler
+	know that dim > 0 to avoid warnings.
+
 2013-11-15  Janne Blomqvist  <jb@gcc.gnu.org>
 	    Jerry DeLisle  <jvdelisle@gcc.gnu.org>
 
diff --git a/libgfortran/intrinsics/unpack_generic.c b/libgfortran/intrinsics/unpack_generic.c
index d06e0a99e27..c57914f06cf 100644
--- a/libgfortran/intrinsics/unpack_generic.c
+++ b/libgfortran/intrinsics/unpack_generic.c
@@ -144,6 +144,9 @@ unpack_internal (gfc_array_char *ret, const gfc_array_char *vector,
   if (empty)
     return;
 
+  /* This assert makes sure GCC knows we can access *stride[0] later.  */
+  assert (dim > 0);
+
   vstride0 = GFC_DESCRIPTOR_STRIDE_BYTES(vector,0);
   rstride0 = rstride[0];
   fstride0 = fstride[0];