diff --git a/file.c b/file.c
index 46d75498dc..f49b46dcbb 100644
--- a/file.c
+++ b/file.c
@@ -2855,6 +2855,7 @@ file_expand_path(VALUE fname, VALUE dname, int abs_mode, VALUE result)
 	tainted = 1;
 	if (isdirsep(s[1]) || s[1] == '\0') {
 	    buf = 0;
+	    b = 0;
 	    rb_str_set_len(result, 0);
 	    if (*++s) ++s;
 	}