diff --git a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts
index 0f8752d..6fe9d27 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts
@@ -73,19 +73,19 @@
     }
   }
 
-  _computeSideBySideSelected(mode: DiffViewMode) {
+  _computeSideBySideSelected(mode?: DiffViewMode) {
     return mode === DiffViewMode.SIDE_BY_SIDE ? 'selected' : '';
   }
 
-  _computeUnifiedSelected(mode: DiffViewMode) {
+  _computeUnifiedSelected(mode?: DiffViewMode) {
     return mode === DiffViewMode.UNIFIED ? 'selected' : '';
   }
 
-  isSideBySideSelected(mode: DiffViewMode) {
+  isSideBySideSelected(mode?: DiffViewMode) {
     return mode === DiffViewMode.SIDE_BY_SIDE;
   }
 
-  isUnifiedSelected(mode: DiffViewMode) {
+  isUnifiedSelected(mode?: DiffViewMode) {
     return mode === DiffViewMode.UNIFIED;
   }