diff --git a/platform/diff-impl/src/com/intellij/diff/comparison/ChunkOptimizer.java b/platform/diff-impl/src/com/intellij/diff/comparison/ChunkOptimizer.java
index b1e97aadbbd5..993b735e39d7 100644
--- a/platform/diff-impl/src/com/intellij/diff/comparison/ChunkOptimizer.java
+++ b/platform/diff-impl/src/com/intellij/diff/comparison/ChunkOptimizer.java
@@ -82,6 +82,9 @@ abstract class ChunkOptimizer<T> {
     int equalForward = expandForward(myData1, myData2, range1.end1, range1.end2, range1.end1 + count2, range1.end2 + count2);
     int equalBackward = expandBackward(myData1, myData2, range2.start1 - count1, range2.start2 - count1, range2.start1, range2.start2);
 
+    // nothing to do
+    if (equalForward == 0 && equalBackward == 0) return;
+
     // merge chunks left [A]B[B] -> [AB]B
     if (equalForward == count2) {
       myRanges.remove(myRanges.size() - 1);
@@ -226,12 +229,12 @@ abstract class ChunkOptimizer<T> {
       List<Line> touchLines = touchSide.select(myData1, myData2);
       int touchStart = touchSide.select(range2.start1, range2.start2);
 
-      int shiftForward = findNextUnimportantLine(touchLines, touchStart, equalForward, 0);
-      int shiftBackward = findPrevUnimportantLine(touchLines, touchStart - 1, equalBackward, 0);
+      int shiftForward = findNextUnimportantLine(touchLines, touchStart, equalForward + 1, 0);
+      int shiftBackward = findPrevUnimportantLine(touchLines, touchStart - 1, equalBackward + 1, 0);
 
       if (shiftForward == -1 && shiftBackward == -1 && myThreshold != 0) {
-        shiftForward = findNextUnimportantLine(touchLines, touchStart, equalForward, myThreshold);
-        shiftBackward = findPrevUnimportantLine(touchLines, touchStart - 1, equalBackward, myThreshold);
+        shiftForward = findNextUnimportantLine(touchLines, touchStart, equalForward + 1, myThreshold);
+        shiftBackward = findPrevUnimportantLine(touchLines, touchStart - 1, equalBackward + 1, myThreshold);
       }
 
       if (shiftForward == 0 || shiftBackward == 0) return 0;
diff --git a/platform/diff-impl/tests/com/intellij/diff/comparison/LineComparisonUtilTest.kt b/platform/diff-impl/tests/com/intellij/diff/comparison/LineComparisonUtilTest.kt
index e97750d310a5..fe4e76b9d7c0 100644
--- a/platform/diff-impl/tests/com/intellij/diff/comparison/LineComparisonUtilTest.kt
+++ b/platform/diff-impl/tests/com/intellij/diff/comparison/LineComparisonUtilTest.kt
@@ -269,6 +269,12 @@ class LineComparisonUtilTest : ComparisonUtilTestBase() {
       testAll()
     }
 
+    lines {
+      ("A_B_o_o_Y_Z_ _A_B_ _ _Y_Z" - "A_B_o_o_Y_Z_ _A_B_u_u_Y_Z_ _A_B_ _ _Y_Z")
+      default(ins(9, 9, 7))
+      testAll()
+    }
+
     lines {
       ("A_B_o_o_ _A_B_z_z" - "A_B_o_o_ _A_B_u_u_ _A_B_z_z")
       default(ins(5, 5, 5))