diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffTable.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffTable.java
index f2237c59e4..1e333210f2 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffTable.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffTable.java
@@ -37,6 +37,7 @@ class DiffTable extends Composite {
   private static final Binder uiBinder = GWT.create(Binder.class);
 
   interface DiffTableStyle extends CssResource {
+    String fullscreen();
     String intralineBg();
     String diff();
     String activeLine();
@@ -107,6 +108,11 @@ class DiffTable extends Composite {
     UIObject.setVisible(fileCommentRow, show
         && (fileCommentPanelA.getBoxCount() > 0
             || fileCommentPanelB.getBoxCount() > 0));
+    if (show) {
+      host.header.removeStyleName(style.fullscreen());
+    } else {
+      host.header.addStyleName(style.fullscreen());
+    }
     host.resizeCodeMirror();
   }
 
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffTable.ui.xml b/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffTable.ui.xml
index bc80bfd7bf..3764cd1840 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffTable.ui.xml
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffTable.ui.xml
@@ -23,6 +23,10 @@ limitations under the License.
     @external .cm-keymap-fat-cursor, CodeMirror-cursor;
     @external .cm-searching, .cm-trailingspace, .cm-tab;
 
+    .fullscreen {
+      border-bottom: 1px solid #ddd;
+    }
+
     .difftable { max-width: 1484px; }
     .difftable .CodeMirror-lines { padding: 0; }
     .difftable .CodeMirror pre {