diff --git a/weed/server/filer_server_handlers_read.go b/weed/server/filer_server_handlers_read.go
index fcd08a79e..718071da1 100644
--- a/weed/server/filer_server_handlers_read.go
+++ b/weed/server/filer_server_handlers_read.go
@@ -70,7 +70,7 @@ func checkPreconditions(w http.ResponseWriter, r *http.Request, entry *filer.Ent
 		}
 	} else if ifModifiedSinceHeader != "" {
 		if t, parseError := time.Parse(http.TimeFormat, ifModifiedSinceHeader); parseError == nil {
-			if t.After(entry.Attr.Mtime) {
+			if !t.Before(entry.Attr.Mtime) {
 				w.WriteHeader(http.StatusNotModified)
 				return true
 			}