diff --git a/libgfortran/runtime/string.c b/libgfortran/runtime/string.c
index 21585f48dc939cb5fcea31b9b7cfb0b1d4272f15..5bc202320c061a3b4050d8b257b4b927815ad8d6 100644
--- a/libgfortran/runtime/string.c
+++ b/libgfortran/runtime/string.c
@@ -242,8 +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),
-		    "integer too large");
+      _Static_assert (sizeof(GFC_UINTEGER_LARGEST) <= 2 * sizeof(uint64_t),
+		      "integer too large");
 
       GFC_UINTEGER_LARGEST r;
       r = n % TEN19;