diff --git a/frame.go b/frame.go
index 7c48fc2f5..e7bfd4a40 100644
--- a/frame.go
+++ b/frame.go
@@ -439,19 +439,21 @@ func (f *Frame) CreateField(field *Field) error {
 	return nil
 }
 
-// GetFields list all the fields.
+// GetFields returns a list of all the fields in the frame.
 func (f *Frame) GetFields() (*FrameSchema, error) {
-	f.mu.Lock()
-	defer f.mu.Unlock()
+	f.mu.RLock()
+	defer f.mu.RUnlock()
 
-	// Ensure frame supports fields.
+	// Ensure the frame supports fields.
 	if !f.RangeEnabled() {
 		return nil, ErrFrameFieldsNotAllowed
 	}
+
 	err := f.loadSchema()
 	if err != nil {
 		return nil, err
 	}
+
 	return f.schema, nil
 }
 
diff --git a/handler.go b/handler.go
index e4c16cb9a..d8463862a 100644
--- a/handler.go
+++ b/handler.go
@@ -119,7 +119,7 @@ func NewRouter(handler *Handler) *mux.Router {
 	router.HandleFunc("/index/{index}/frame/{frame}/restore", handler.handlePostFrameRestore).Methods("POST")
 	router.HandleFunc("/index/{index}/frame/{frame}/time-quantum", handler.handlePatchFrameTimeQuantum).Methods("PATCH")
 	router.HandleFunc("/index/{index}/frame/{frame}/field/{field}", handler.handlePostFrameField).Methods("POST")
-	router.HandleFunc("/index/{index}/frame/{frame}/fields", handler.handleGetFrameField).Methods("GET")
+	router.HandleFunc("/index/{index}/frame/{frame}/fields", handler.handleGetFrameFields).Methods("GET")
 	router.HandleFunc("/index/{index}/frame/{frame}/field/{field}", handler.handleDeleteFrameField).Methods("DELETE")
 	router.HandleFunc("/index/{index}/frame/{frame}/views", handler.handleGetFrameViews).Methods("GET")
 	router.HandleFunc("/index/{index}/frame/{frame}/view/{view}", handler.handleDeleteView).Methods("DELETE")
@@ -843,12 +843,22 @@ func (h *Handler) handleDeleteFrameField(w http.ResponseWriter, r *http.Request)
 	}
 }
 
-func (h *Handler) handleGetFrameField(w http.ResponseWriter, r *http.Request) {
+func (h *Handler) handleGetFrameFields(w http.ResponseWriter, r *http.Request) {
 	indexName := mux.Vars(r)["index"]
 	frameName := mux.Vars(r)["frame"]
 
 	index := h.Holder.index(indexName)
+	if index == nil {
+		http.Error(w, ErrIndexNotFound.Error(), http.StatusNotFound)
+		return
+	}
+
 	frame := index.frame(frameName)
+	if frame == nil {
+		http.Error(w, ErrFrameNotFound.Error(), http.StatusNotFound)
+		return
+	}
+
 	schema, err := frame.GetFields()
 	if err == ErrFrameFieldsNotAllowed {
 		http.Error(w, err.Error(), http.StatusBadRequest)
@@ -857,6 +867,7 @@ func (h *Handler) handleGetFrameField(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
+
 	// Encode response.
 	if err := json.NewEncoder(w).Encode(getFrameFieldsResponse{Fields: schema.Fields}); err != nil {
 		h.logger().Printf("response encoding error: %s", err)