diff --git a/gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/Change.java b/gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/Change.java
index 26bab58bdd..863ed0870f 100644
--- a/gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/Change.java
+++ b/gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/Change.java
@@ -572,6 +572,10 @@ public final class Change {
     return originalSubject != null ? originalSubject : subject;
   }
 
+  public String getOriginalSubjectOrNull() {
+    return originalSubject;
+  }
+
   /** Get the id of the most current {@link PatchSet} in this change. */
   public PatchSet.Id currentPatchSetId() {
     if (currentPatchSetId > 0) {
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/notedb/ChangeBundle.java b/gerrit-server/src/main/java/com/google/gerrit/server/notedb/ChangeBundle.java
index e6332ea0a4..8654834868 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/notedb/ChangeBundle.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/notedb/ChangeBundle.java
@@ -312,8 +312,24 @@ public class ChangeBundle {
     Change a = bundleA.change;
     Change b = bundleB.change;
     String desc = a.getId().equals(b.getId()) ? describe(a.getId()) : "Changes";
+
+    boolean excludeOrigSubj = false;
+    // Ignore null original subject on the ReviewDb side, as this field is
+    // always set in NoteDb.
+    if (bundleA.source == REVIEW_DB && bundleB.source == NOTE_DB
+        && a.getOriginalSubjectOrNull() == null) {
+      excludeOrigSubj = true;
+    } else if (bundleA.source == NOTE_DB && bundleB.source == REVIEW_DB
+        && b.getOriginalSubjectOrNull() == null) {
+      excludeOrigSubj = true;
+    }
+
+    List<String> exclude = Lists.newArrayList("rowVersion", "noteDbState");
+    if (excludeOrigSubj) {
+      exclude.add("originalSubject");
+    }
     diffColumnsExcluding(diffs, Change.class, desc, bundleA, a, bundleB, b,
-        "rowVersion", "noteDbState");
+        exclude);
   }
 
   private static void diffChangeMessages(List<String> diffs,
diff --git a/gerrit-server/src/test/java/com/google/gerrit/server/notedb/ChangeBundleTest.java b/gerrit-server/src/test/java/com/google/gerrit/server/notedb/ChangeBundleTest.java
index ea12ecaffe..f3a6698046 100644
--- a/gerrit-server/src/test/java/com/google/gerrit/server/notedb/ChangeBundleTest.java
+++ b/gerrit-server/src/test/java/com/google/gerrit/server/notedb/ChangeBundleTest.java
@@ -181,6 +181,51 @@ public class ChangeBundleTest {
     assertDiffs(b3, b1, msg);
   }
 
+  @Test
+  public void diffChangesIgnoresNullOriginalSubjectInReviewDb()
+      throws Exception {
+    Change c1 = TestChanges.newChange(
+        new Project.NameKey("project"), new Account.Id(100));
+    c1.setCurrentPatchSet(c1.currentPatchSetId(), "Subject", null);
+    Change c2 = clone(c1);
+    c2.setCurrentPatchSet(
+        c2.currentPatchSetId(), c1.getSubject(), "Original subject");
+
+    // Both ReviewDb, exact match required.
+    ChangeBundle b1 = new ChangeBundle(c1, messages(), patchSets(), approvals(),
+        comments(), REVIEW_DB);
+    ChangeBundle b2 = new ChangeBundle(c2, messages(), patchSets(), approvals(),
+        comments(), REVIEW_DB);
+    assertDiffs(b1, b2,
+        "originalSubject differs for Change.Id " + c1.getId() + ":"
+            + " {null} != {Original subject}");
+
+    // Both NoteDb, exact match required.
+    b1 = new ChangeBundle(c1, messages(), patchSets(), approvals(), comments(),
+        NOTE_DB);
+    b2 = new ChangeBundle(c2, messages(), patchSets(), approvals(), comments(),
+        NOTE_DB);
+    assertDiffs(b1, b2,
+        "originalSubject differs for Change.Id " + c1.getId() + ":"
+            + " {null} != {Original subject}");
+
+    // Original subject ignored if ReviewDb has null value.
+    b1 = new ChangeBundle(c1, messages(), patchSets(), approvals(), comments(),
+        REVIEW_DB);
+    b2 = new ChangeBundle(c2, messages(), patchSets(), approvals(), comments(),
+        NOTE_DB);
+    assertNoDiffs(b1, b2);
+
+    // Exact match still required if NoteDb has null value (not realistic).
+    b1 = new ChangeBundle(c1, messages(), patchSets(), approvals(), comments(),
+        NOTE_DB);
+    b2 = new ChangeBundle(c2, messages(), patchSets(), approvals(), comments(),
+        REVIEW_DB);
+    assertDiffs(b1, b2,
+        "originalSubject differs for Change.Id " + c1.getId() + ":"
+            + " {null} != {Original subject}");
+  }
+
   @Test
   public void diffChangeMessageKeySets() throws Exception {
     Change c = TestChanges.newChange(project, accountId);