@@ -14,11 +14,10 @@
  * file.
  */
 
 #include "config.h"
 
-#include <ctype.h>
 #include <errno.h>
 #include <stdarg.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -1665,12 +1664,12 @@
 				      withString: @"\\\n"];
 
 		if (options & OF_JSON_REPRESENTATION_IDENTIFIER) {
 			const char *cString = [self UTF8String];
 
-			if ((!isalpha((int)cString[0]) && cString[0] != '_' &&
-			    cString[0] != '$') ||
+			if ((!of_ascii_isalpha(cString[0]) &&
+			    cString[0] != '_' && cString[0] != '$') ||
 			    strpbrk(cString, " \n\r\t\b\f\\\"'") != NULL) {
 				[JSON prependString: @"\""];
 				[JSON appendString: @"\""];
 			}
 		} else {