diff --git a/handler.go b/handler.go
index ffd28da46..02d20564c 100644
--- a/handler.go
+++ b/handler.go
@@ -122,7 +122,7 @@ func BuildRouters(handler *Handler) {
 
 func (h *Handler) populateValidators() {
 	h.validators = map[string]*queryValidationSpec{}
-	h.validators["GetFragmentNodes"] = QueryValidationSpecRequired("slice").Optional("index")
+	h.validators["GetFragmentNodes"] = QueryValidationSpecRequired("slice", "index")
 	h.validators["GetSliceMax"] = QueryValidationSpecRequired().Optional("inverse")
 	h.validators["PostQuery"] = QueryValidationSpecRequired().Optional("slices", "columnAttrs", "excludeAttrs", "excludeBits")
 	h.validators["GetExport"] = QueryValidationSpecRequired("index", "frame", "view", "slice")
diff --git a/handler_test.go b/handler_test.go
index ba9480544..12c145e87 100644
--- a/handler_test.go
+++ b/handler_test.go
@@ -1225,6 +1225,13 @@ func TestHandler_Fragment_Nodes(t *testing.T) {
 		t.Fatalf("unexpected status code: %d", w.Code)
 	}
 
+	// index is required
+	w = httptest.NewRecorder()
+	r = test.MustNewHTTPRequest("GET", "/fragment/nodes?slice=0", nil)
+	h.ServeHTTP(w, r)
+	if w.Code != http.StatusBadRequest {
+		t.Fatalf("unexpected status code: %d", w.Code)
+	}
 }
 
 // Ensure the handler can return expvars without panicking.