diff --git a/java/com/google/gerrit/server/restapi/change/PostReview.java b/java/com/google/gerrit/server/restapi/change/PostReview.java
index a360510..562bdf8 100644
--- a/java/com/google/gerrit/server/restapi/change/PostReview.java
+++ b/java/com/google/gerrit/server/restapi/change/PostReview.java
@@ -1272,28 +1272,27 @@
             del.add(c);
             update.putApproval(normName, (short) 0);
           }
-        } else if (c != null) {
-          // Check if the label exists in the request input (the user voted again). If the user
-          // hadn't voted again, there is no need to re-apply the vote.
-          if (inLabels.keySet().contains(c.label())) {
-            PatchSetApproval.Builder b =
-                c.toBuilder()
-                    .value(ent.getValue())
-                    .granted(ctx.getWhen())
-                    .tag(Optional.ofNullable(in.tag));
-            ctx.getUser().updateRealAccountId(b::realAccountId);
-            c = b.build();
-            ups.add(c);
-            addLabelDelta(normName, c.value());
-            oldApprovals.put(normName, previous.get(normName));
-            approvals.put(normName, c.value());
-            update.putApproval(normName, ent.getValue());
-          } else {
-            current.put(normName, c);
-            oldApprovals.put(normName, null);
-            approvals.put(normName, c.value());
-          }
-        } else {
+          // Only allow voting again if the vote is copied over from a past patch-set, or the
+          // values are different.
+        } else if (c != null
+            && (c.value() != ent.getValue() || isApprovalCopiedOver(c, ctx.getNotes()))) {
+          PatchSetApproval.Builder b =
+              c.toBuilder()
+                  .value(ent.getValue())
+                  .granted(ctx.getWhen())
+                  .tag(Optional.ofNullable(in.tag));
+          ctx.getUser().updateRealAccountId(b::realAccountId);
+          c = b.build();
+          ups.add(c);
+          addLabelDelta(normName, c.value());
+          oldApprovals.put(normName, previous.get(normName));
+          approvals.put(normName, c.value());
+          update.putApproval(normName, ent.getValue());
+        } else if (c != null && c.value() == ent.getValue()) {
+          current.put(normName, c);
+          oldApprovals.put(normName, null);
+          approvals.put(normName, c.value());
+        } else if (c == null) {
           c =
               ApprovalsUtil.newApproval(psId, user, lt.getLabelId(), ent.getValue(), ctx.getWhen())
                   .tag(Optional.ofNullable(in.tag))
@@ -1319,6 +1318,17 @@
       return !del.isEmpty() || !ups.isEmpty();
     }
 
+    /**
+     * Approval is copied over if it doesn't exist in the approvals of the current patch-set
+     * according to change notes (which means it was computed in {@link
+     * com.google.gerrit.server.ApprovalInference})
+     */
+    private boolean isApprovalCopiedOver(
+        PatchSetApproval patchSetApproval, ChangeNotes changeNotes) {
+      return !changeNotes.getApprovals().get(changeNotes.getChange().currentPatchSetId()).stream()
+          .anyMatch(p -> p.equals(patchSetApproval));
+    }
+
     private void validatePostSubmitLabels(
         ChangeContext ctx,
         LabelTypes labelTypes,
diff --git a/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java b/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java
index 0b2e0f7..c8b1715 100644
--- a/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java
@@ -63,7 +63,6 @@
 import com.google.gerrit.server.restapi.change.OnPostReview;
 import com.google.gerrit.server.restapi.change.PostReview;
 import com.google.gerrit.server.update.CommentsRejectedException;
-import com.google.gerrit.testing.FakeEmailSender;
 import com.google.gerrit.testing.TestCommentHelper;
 import com.google.inject.Inject;
 import com.google.inject.Module;
@@ -597,7 +596,7 @@
       input = new ReviewInput().label(LabelId.CODE_REVIEW, 2);
       gApi.changes().id(r.getChangeId()).current().review(input);
       testOnPostReview.assertApproval(
-          LabelId.CODE_REVIEW, /* expectedOldValue= */ 2, /* expectedNewValue= */ 2);
+          LabelId.CODE_REVIEW, /* expectedOldValue= */ null, /* expectedNewValue= */ 2);
 
       // Delete the vote.
       input = new ReviewInput().label(LabelId.CODE_REVIEW, 0);
@@ -627,21 +626,19 @@
     assertThat(r.getChange().approvals().values()).hasSize(1);
     List<ChangeMessageInfo> changeMessages = gApi.changes().id(r.getChangeId()).messages();
 
-    // The two latest change messages are both about Code-Review+2
+    // Only the last change message is about Code-Review+2
     assertThat(Iterables.getLast(changeMessages).message).isEqualTo("Patch Set 1: Code-Review+2");
     changeMessages.remove(changeMessages.size() - 1);
-    assertThat(Iterables.getLast(changeMessages).message).isEqualTo("Patch Set 1: Code-Review+2");
+    assertThat(Iterables.getLast(changeMessages).message)
+        .isNotEqualTo("Patch Set 1: Code-Review+2");
 
-    // The two latest emails are about Code-Review +2.
-    List<FakeEmailSender.Message> messages = sender.getMessages();
-    assertThat(messages).hasSize(2);
-    for (FakeEmailSender.Message message : messages) {
-      assertThat(message.body()).contains("Patch Set 1: Code-Review+2");
-    }
+    // Only one email is about Code-Review +2 was sent.
+    assertThat(Iterables.getOnlyElement(sender.getMessages()).body())
+        .contains("Patch Set 1: Code-Review+2");
   }
 
   @Test
-  public void votingTheSameVoteSecondTimeExtendsOnPostReview() throws Exception {
+  public void votingTheSameVoteSecondTimeExtendsOnPostReviewWithOldNullValue() throws Exception {
     PushOneCommit.Result r = createChange();
 
     // Add a new vote.
@@ -656,12 +653,12 @@
       gApi.changes().id(r.getChangeId()).current().review(input);
 
       testOnPostReview.assertApproval(
-          LabelId.CODE_REVIEW, /* expectedOldValue= */ 2, /* expectedNewValue= */ 2);
+          LabelId.CODE_REVIEW, /* expectedOldValue= */ null, /* expectedNewValue= */ 2);
     }
   }
 
   @Test
-  public void votingTheSameVoteSecondTimeFiresOnCommentAdded() throws Exception {
+  public void votingTheSameVoteSecondTimeDoesNotFireOnCommentAdded() throws Exception {
     PushOneCommit.Result r = createChange();
 
     // Add a new vote.
@@ -675,8 +672,8 @@
       input = new ReviewInput().label(LabelId.CODE_REVIEW, 2);
       gApi.changes().id(r.getChangeId()).current().review(input);
 
-      assertThat(testListener.lastCommentAddedEvent.getComment())
-          .isEqualTo("Patch Set 1: Code-Review+2");
+      // Event not fired.
+      assertThat(testListener.lastCommentAddedEvent).isNull();
     }
   }
 
diff --git a/javatests/com/google/gerrit/acceptance/api/revision/RevisionIT.java b/javatests/com/google/gerrit/acceptance/api/revision/RevisionIT.java
index 0d92c60..9bdbd20 100644
--- a/javatests/com/google/gerrit/acceptance/api/revision/RevisionIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/revision/RevisionIT.java
@@ -180,12 +180,12 @@
     assertThat(approval.postSubmit).isNull();
     assertPermitted(gApi.changes().id(changeId).get(DETAILED_LABELS), LabelId.CODE_REVIEW, 1, 2);
 
-    // Repeating the current label is allowed. Flips the postSubmit since technically this is a
-    // new vote.
+    // Repeating the current label is allowed. Does not flip the postSubmit bit due to
+    // deduplication codepath.
     gApi.changes().id(changeId).current().review(ReviewInput.recommend());
     approval = getApproval(changeId, label);
     assertThat(approval.value).isEqualTo(1);
-    assertThat(approval.postSubmit).isTrue();
+    assertThat(approval.postSubmit).isNull();
 
     // Reducing vote is not allowed.
     ResourceConflictException thrown =
@@ -197,7 +197,7 @@
         .isEqualTo("Cannot reduce vote on labels for closed change: Code-Review");
     approval = getApproval(changeId, label);
     assertThat(approval.value).isEqualTo(1);
-    assertThat(approval.postSubmit).isTrue();
+    assertThat(approval.postSubmit).isNull();
 
     // Increasing vote is allowed.
     gApi.changes().id(changeId).current().review(ReviewInput.approve());