1 files changed, 2 insertions, 1 deletions
diff --git a/src/expr.c b/src/expr.c
index 3ecec0735..5a680d2ec 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -35,6 +35,7 @@
 
 #include <gmp.h>
 #include <regex.h>
+#include "c-ctype.h"
 #include "long-options.h"
 #include "mcel.h"
 #include "strnumcmp.h"
@@ -439,7 +440,7 @@ looks_like_integer (char const *cp)
   cp += (*cp == '-');
 
   do
-    if (! ISDIGIT (*cp))
+    if (! c_isdigit (*cp))
       return false;
   while (*++cp);