diff --git a/src/misc1.c b/src/misc1.c
index 019bbaf..d369f2a 100644
--- a/src/misc1.c
+++ b/src/misc1.c
@@ -2699,11 +2699,11 @@
     // non-URL text.
 
     // first character must be alpha
-    if (!isalpha(*fname))
+    if (!ASCII_ISALPHA(*fname))
 	return 0;
 
     // check body: alpha or dash
-    for (p = fname + 1; (isalpha(*p) || (*p == '-')); ++p)
+    for (p = fname + 1; (ASCII_ISALPHA(*p) || (*p == '-')); ++p)
 	;
 
     // check last char is not a dash