diff --git a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerApprovalCheck.java b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerApprovalCheck.java
index a49620b..5f55f62 100644
--- a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerApprovalCheck.java
+++ b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerApprovalCheck.java
@@ -14,7 +14,6 @@
 
 package com.google.gerrit.plugins.codeowners.backend;
 
-import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static java.util.Objects.requireNonNull;
@@ -27,6 +26,7 @@
 import com.google.gerrit.entities.PatchSetApproval;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.exceptions.StorageException;
+import com.google.gerrit.extensions.restapi.ResourceConflictException;
 import com.google.gerrit.plugins.codeowners.api.CodeOwnerStatus;
 import com.google.gerrit.plugins.codeowners.config.CodeOwnersPluginConfiguration;
 import com.google.gerrit.plugins.codeowners.config.RequiredApproval;
@@ -106,7 +106,7 @@
    * @return whether the given change has sufficient code owner approvals to be submittable
    */
   public boolean isSubmittable(ChangeNotes changeNotes)
-      throws IOException, PatchListNotAvailableException {
+      throws ResourceConflictException, IOException, PatchListNotAvailableException {
     requireNonNull(changeNotes, "changeNotes");
     logger.atFine().log(
         "checking if change %d in project %s is submittable",
@@ -156,7 +156,7 @@
    *     returned
    */
   public Stream<FileCodeOwnerStatus> getFileStatuses(ChangeNotes changeNotes)
-      throws IOException, PatchListNotAvailableException {
+      throws ResourceConflictException, IOException, PatchListNotAvailableException {
     requireNonNull(changeNotes, "changeNotes");
     try (TraceTimer traceTimer =
         TraceContext.newTimer(
@@ -636,16 +636,18 @@
    *
    * <p>This is the revision from which the code owner configs should be read when computing code
    * owners for the files that are touched in the change.
+   *
+   * @throws ResourceConflictException thrown if the destination branch is not found, e.g. when the
+   *     branch got deleted after the change was created
    */
-  private ObjectId getDestBranchRevision(Change change) throws IOException {
+  private ObjectId getDestBranchRevision(Change change)
+      throws IOException, ResourceConflictException {
     try (Repository repository = repoManager.openRepository(change.getProject());
         RevWalk rw = new RevWalk(repository)) {
       Ref ref = repository.exactRef(change.getDest().branch());
-      checkNotNull(
-          ref,
-          "branch %s in repository %s not found",
-          change.getDest().branch(),
-          change.getProject().get());
+      if (ref == null) {
+        throw new ResourceConflictException("destination branch not found");
+      }
       return rw.parseCommit(ref.getObjectId());
     }
   }
diff --git a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerSubmitRule.java b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerSubmitRule.java
index c1a21a1..f179a9c 100644
--- a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerSubmitRule.java
+++ b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerSubmitRule.java
@@ -22,6 +22,7 @@
 import com.google.gerrit.entities.SubmitRequirement;
 import com.google.gerrit.extensions.annotations.Exports;
 import com.google.gerrit.extensions.config.FactoryModule;
+import com.google.gerrit.extensions.restapi.ResourceConflictException;
 import com.google.gerrit.plugins.codeowners.config.CodeOwnersPluginConfiguration;
 import com.google.gerrit.server.logging.Metadata;
 import com.google.gerrit.server.logging.TraceContext;
@@ -98,7 +99,7 @@
   }
 
   private SubmitRecord getSubmitRecord(ChangeNotes changeNotes)
-      throws IOException, PatchListNotAvailableException {
+      throws ResourceConflictException, IOException, PatchListNotAvailableException {
     requireNonNull(changeNotes, "changeNotes");
     return codeOwnerApprovalCheck.isSubmittable(changeNotes) ? ok() : notReady();
   }
diff --git a/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnerApprovalCheckTest.java b/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnerApprovalCheckTest.java
index dc2549f..1249301 100644
--- a/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnerApprovalCheckTest.java
+++ b/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnerApprovalCheckTest.java
@@ -22,13 +22,17 @@
 import static com.google.gerrit.server.group.SystemGroupBackend.REGISTERED_USERS;
 import static com.google.gerrit.testing.GerritJUnit.assertThrows;
 
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.gerrit.acceptance.TestAccount;
 import com.google.gerrit.acceptance.config.GerritConfig;
 import com.google.gerrit.acceptance.testsuite.project.ProjectOperations;
 import com.google.gerrit.acceptance.testsuite.request.RequestScopeOperations;
+import com.google.gerrit.entities.BranchNameKey;
 import com.google.gerrit.entities.Change;
 import com.google.gerrit.extensions.api.changes.ReviewInput;
+import com.google.gerrit.extensions.api.projects.DeleteBranchesInput;
+import com.google.gerrit.extensions.restapi.ResourceConflictException;
 import com.google.gerrit.plugins.codeowners.JgitPath;
 import com.google.gerrit.plugins.codeowners.acceptance.AbstractCodeOwnersTest;
 import com.google.gerrit.plugins.codeowners.acceptance.testsuite.CodeOwnerConfigOperations;
@@ -1848,6 +1852,24 @@
     }
   }
 
+  @Test
+  public void getStatus_branchDeleted() throws Exception {
+    String branchName = "tempBranch";
+    createBranch(BranchNameKey.create(project, branchName));
+
+    String changeId = createChange("refs/for/" + branchName).getChangeId();
+
+    DeleteBranchesInput input = new DeleteBranchesInput();
+    input.branches = ImmutableList.of(branchName);
+    gApi.projects().name(project.get()).deleteBranches(input);
+
+    ResourceConflictException exception =
+        assertThrows(
+            ResourceConflictException.class,
+            () -> codeOwnerApprovalCheck.getFileStatuses(getChangeNotes(changeId)));
+    assertThat(exception).hasMessageThat().isEqualTo("destination branch not found");
+  }
+
   private ChangeNotes getChangeNotes(String changeId) throws Exception {
     return changeNotesFactory.create(project, Change.id(gApi.changes().id(changeId).get()._number));
   }
diff --git a/resources/Documentation/rest-api.md b/resources/Documentation/rest-api.md
index abc4bfe..fdcd4da 100644
--- a/resources/Documentation/rest-api.md
+++ b/resources/Documentation/rest-api.md
@@ -340,6 +340,11 @@
   }
 ```
 
+If the destination branch of a change no longer exists (e.g. because it was
+deleted), `409 Conflict` is returned. Since the code owners are retrieved from
+the destination branch, computing the code owner status is not possible, if the
+destination branch is missing.
+
 ## <a id="revision-endpoints"> Revision Endpoints
 
 ### <a id="list-code-owners-for-path-in-change"> List Code Owners for path in change