diff --git a/platform/diff-impl/src/com/intellij/diff/actions/ProxyUndoRedoAction.java b/platform/diff-impl/src/com/intellij/diff/actions/ProxyUndoRedoAction.java
new file mode 100644
index 000000000000..1e7a30f62c59
--- /dev/null
+++ b/platform/diff-impl/src/com/intellij/diff/actions/ProxyUndoRedoAction.java
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2000-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.intellij.diff.actions;
+
+import com.intellij.openapi.actionSystem.AnActionEvent;
+import com.intellij.openapi.actionSystem.EmptyAction;
+import com.intellij.openapi.actionSystem.IdeActions;
+import com.intellij.openapi.command.undo.UndoManager;
+import com.intellij.openapi.editor.Editor;
+import com.intellij.openapi.fileEditor.TextEditor;
+import com.intellij.openapi.fileEditor.impl.text.TextEditorProvider;
+import com.intellij.openapi.project.DumbAwareAction;
+import com.intellij.openapi.project.Project;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import javax.swing.*;
+
+public class ProxyUndoRedoAction extends DumbAwareAction {
+  @NotNull private final UndoManager myUndoManager;
+  @NotNull private final TextEditor myEditor;
+  private final boolean myUndo;
+
+  private ProxyUndoRedoAction(@NotNull UndoManager manager, @NotNull TextEditor editor, boolean undo) {
+    myUndoManager = manager;
+    myEditor = editor;
+    myUndo = undo;
+  }
+
+  public static void register(@Nullable Project project, @NotNull Editor editor, @NotNull JComponent component) {
+    UndoManager undoManager = project != null ? UndoManager.getInstance(project) : UndoManager.getGlobalInstance();
+    TextEditor textEditor = TextEditorProvider.getInstance().getTextEditor(editor);
+    if (undoManager != null) {
+      EmptyAction.setupAction(new ProxyUndoRedoAction(undoManager, textEditor, true), IdeActions.ACTION_UNDO, component);
+      EmptyAction.setupAction(new ProxyUndoRedoAction(undoManager, textEditor, false), IdeActions.ACTION_REDO, component);
+    }
+  }
+
+  @Override
+  public void update(AnActionEvent e) {
+    e.getPresentation().setEnabled(myUndo ? myUndoManager.isUndoAvailable(myEditor) : myUndoManager.isRedoAvailable(myEditor));
+  }
+
+  @Override
+  public void actionPerformed(AnActionEvent e) {
+    if (myUndo) {
+      myUndoManager.undo(myEditor);
+    }
+    else {
+      myUndoManager.redo(myEditor);
+    }
+  }
+}
diff --git a/platform/diff-impl/src/com/intellij/diff/merge/TextMergeTool.java b/platform/diff-impl/src/com/intellij/diff/merge/TextMergeTool.java
index b9a812426e9c..38b3e8e85389 100644
--- a/platform/diff-impl/src/com/intellij/diff/merge/TextMergeTool.java
+++ b/platform/diff-impl/src/com/intellij/diff/merge/TextMergeTool.java
@@ -17,6 +17,7 @@ package com.intellij.diff.merge;
 
 import com.intellij.diff.DiffContext;
 import com.intellij.diff.FrameDiffTool;
+import com.intellij.diff.actions.ProxyUndoRedoAction;
 import com.intellij.diff.comparison.ByLine;
 import com.intellij.diff.comparison.ComparisonMergeUtil;
 import com.intellij.diff.comparison.ComparisonPolicy;
@@ -44,8 +45,6 @@ import com.intellij.openapi.editor.Document;
 import com.intellij.openapi.editor.Editor;
 import com.intellij.openapi.editor.event.DocumentEvent;
 import com.intellij.openapi.editor.ex.EditorEx;
-import com.intellij.openapi.fileEditor.TextEditor;
-import com.intellij.openapi.fileEditor.impl.text.TextEditorProvider;
 import com.intellij.openapi.progress.ProcessCanceledException;
 import com.intellij.openapi.progress.ProgressIndicator;
 import com.intellij.openapi.progress.ProgressManager;
@@ -225,10 +224,7 @@ public class TextMergeTool implements MergeTool {
         DiffUtil.registerAction(new IgnoreSelectedChangesAction(Side.LEFT, true), myPanel);
         DiffUtil.registerAction(new IgnoreSelectedChangesAction(Side.RIGHT, true), myPanel);
 
-        if (myUndoManager != null) {
-          new UndoRedoAction(true).register();
-          new UndoRedoAction(false).register();
-        }
+        ProxyUndoRedoAction.register(getProject(), getEditor(ThreeSide.BASE), myContentPanel);
       }
 
       @Override
@@ -1161,43 +1157,6 @@ public class TextMergeTool implements MergeTool {
       // Helpers
       //
 
-      private class UndoRedoAction extends DumbAwareAction {
-        private final boolean myUndo;
-
-        public UndoRedoAction(boolean undo) {
-          myUndo = undo;
-        }
-
-        public void register() {
-          EmptyAction.setupAction(this, myUndo ? IdeActions.ACTION_UNDO : IdeActions.ACTION_REDO, myContentPanel);
-        }
-
-        @Override
-        public void update(AnActionEvent e) {
-          assert myUndoManager != null;
-          TextEditor textEditor = getTextEditor();
-          e.getPresentation().setEnabled(myUndo ? myUndoManager.isUndoAvailable(textEditor) : myUndoManager.isRedoAvailable(textEditor));
-        }
-
-        @Override
-        public void actionPerformed(AnActionEvent e) {
-          assert myUndoManager != null;
-          TextEditor textEditor = getTextEditor();
-          if (myUndo) {
-            myUndoManager.undo(textEditor);
-          }
-          else {
-            myUndoManager.redo(textEditor);
-          }
-        }
-
-        @NotNull
-        private TextEditor getTextEditor() {
-          EditorEx editor = getEditor(ThreeSide.BASE);
-          return TextEditorProvider.getInstance().getTextEditor(editor);
-        }
-      }
-
       private class MyDividerPaintable implements DiffDividerDrawUtil.DividerPaintable {
         @NotNull private final Side mySide;
 
diff --git a/platform/diff-impl/src/com/intellij/diff/tools/util/side/TwosideTextDiffViewer.java b/platform/diff-impl/src/com/intellij/diff/tools/util/side/TwosideTextDiffViewer.java
index 066d2710ff58..ff6e13e39a3f 100644
--- a/platform/diff-impl/src/com/intellij/diff/tools/util/side/TwosideTextDiffViewer.java
+++ b/platform/diff-impl/src/com/intellij/diff/tools/util/side/TwosideTextDiffViewer.java
@@ -16,6 +16,7 @@
 package com.intellij.diff.tools.util.side;
 
 import com.intellij.diff.DiffContext;
+import com.intellij.diff.actions.ProxyUndoRedoAction;
 import com.intellij.diff.actions.impl.FocusOppositePaneAction;
 import com.intellij.diff.actions.impl.OpenInEditorWithMouseAction;
 import com.intellij.diff.actions.impl.SetEditorSettingsAction;
@@ -80,6 +81,12 @@ public abstract class TwosideTextDiffViewer extends TwosideDiffViewer<TextEditor
     myEditableEditors = TextDiffViewerUtil.getEditableEditors(getEditors());
 
     TextDiffViewerUtil.checkDifferentDocuments(myRequest);
+
+    boolean editable1 = DiffUtil.canMakeWritable(getContent1().getDocument());
+    boolean editable2 = DiffUtil.canMakeWritable(getContent2().getDocument());
+    if (editable1 ^ editable2) {
+      ProxyUndoRedoAction.register(getProject(), editable1 ? getEditor1() : getEditor2(), myPanel);
+    }
   }
 
   @Override