diff --git a/libgfortran/runtime/string.c b/libgfortran/runtime/string.c
index 0ccd731852abca1c0b28585684bde4d39f5f7311..21585f48dc939cb5fcea31b9b7cfb0b1d4272f15 100644
--- a/libgfortran/runtime/string.c
+++ b/libgfortran/runtime/string.c
@@ -242,7 +242,8 @@ gfc_itoa (GFC_UINTEGER_LARGEST n, char *buffer, size_t len)
 	 integers (we would need three calls), but they do suffice for all
 	 values up to 2^127, which is the largest that Fortran can produce
 	 (-HUGE(0_16)-1) with its signed integer types.  */
-      static_assert(sizeof(GFC_UINTEGER_LARGEST) <= 2 * sizeof(uint64_t));
+      static_assert(sizeof(GFC_UINTEGER_LARGEST) <= 2 * sizeof(uint64_t),
+		    "integer too large");
 
       GFC_UINTEGER_LARGEST r;
       r = n % TEN19;