diff --git a/contrib/win32/win32compat/misc.c b/contrib/win32/win32compat/misc.c
index 2e8a8f52f..552c19f09 100644
--- a/contrib/win32/win32compat/misc.c
+++ b/contrib/win32/win32compat/misc.c
@@ -1391,7 +1391,7 @@ is_absolute_path(const char *path)
 	if(*path == '\"' || *path == '\'') /* skip double quote if path is "c:\abc" */
 		path++;
 
-	if (*path == '/' || *path == '\\' || (*path != '\0' && isalpha(*path) && path[1] == ':') ||
+	if (*path == '/' || *path == '\\' || (*path != '\0' && __isascii(*path) && isalpha(*path) && path[1] == ':') ||
 	    ((strlen(path) >= strlen(PROGRAM_DATA)) && (memcmp(path, PROGRAM_DATA, strlen(PROGRAM_DATA)) == 0)))
 		retVal = 1;