diff --git a/include/flatcc/portable/grisu3_print.h b/include/flatcc/portable/grisu3_print.h
index 6c4d9e9a..4f71985c 100644
--- a/include/flatcc/portable/grisu3_print.h
+++ b/include/flatcc/portable/grisu3_print.h
@@ -183,7 +183,7 @@ static int grisu3_i_to_str(int val, char *str)
 
 static int grisu3_print_nan(uint64_t v, char *dst)
 {
-    static char hexdigits[] = "0123456789ABCDEF";
+    static char hexdigits[17] = "0123456789ABCDEF";
     int i = 0;
 
     dst[0] = 'N';