diff --git a/src/highlight.c b/src/highlight.c
index 31c3280..318564c 100644
--- a/src/highlight.c
+++ b/src/highlight.c
@@ -2307,7 +2307,7 @@
     static int
 hex_digit(int c)
 {
-    if (isdigit(c))
+    if (SAFE_isdigit(c))
 	return c - '0';
     c = TOLOWER_ASC(c);
     if (c >= 'a' && c <= 'f')