1 files changed, 1 insertions, 1 deletions
diff --git a/file.c b/file.c
index d812d7fedc..2e465e2d89 100644
--- a/file.c
+++ b/file.c
@@ -2789,7 +2789,7 @@ rb_file_join(ary, sep)
 	name = StringValueCStr(result);
 	if (i > 0 && !NIL_P(sep)) {
 	    tail = chompdirsep(name);
-	    if (isdirsep(RSTRING(tmp)->ptr[0])) {
+	    if (RSTRING(tmp)->ptr && isdirsep(RSTRING(tmp)->ptr[0])) {
 		RSTRING(result)->len = tail - name;
 	    }
 	    else if (!*tail) {