diff --git a/java/com/google/gerrit/plugins/codeowners/api/CodeOwnerProjectConfigInput.java b/java/com/google/gerrit/plugins/codeowners/api/CodeOwnerProjectConfigInput.java
index cfb2904..5d899f3 100644
--- a/java/com/google/gerrit/plugins/codeowners/api/CodeOwnerProjectConfigInput.java
+++ b/java/com/google/gerrit/plugins/codeowners/api/CodeOwnerProjectConfigInput.java
@@ -37,4 +37,7 @@
    * <p>Overrides any existing disabled branch configuration.
    */
   public List<String> disabledBranches;
+
+  /** The file extension that should be used for code owner config files in this project. */
+  public String fileExtension;
 }
diff --git a/java/com/google/gerrit/plugins/codeowners/restapi/PutCodeOwnerProjectConfig.java b/java/com/google/gerrit/plugins/codeowners/restapi/PutCodeOwnerProjectConfig.java
index fba8766..91543a6 100644
--- a/java/com/google/gerrit/plugins/codeowners/restapi/PutCodeOwnerProjectConfig.java
+++ b/java/com/google/gerrit/plugins/codeowners/restapi/PutCodeOwnerProjectConfig.java
@@ -15,6 +15,7 @@
 package com.google.gerrit.plugins.codeowners.restapi;
 
 import static com.google.gerrit.plugins.codeowners.backend.config.CodeOwnersPluginConfiguration.SECTION_CODE_OWNERS;
+import static com.google.gerrit.plugins.codeowners.backend.config.GeneralConfig.KEY_FILE_EXTENSION;
 import static com.google.gerrit.plugins.codeowners.backend.config.StatusConfig.KEY_DISABLED;
 import static com.google.gerrit.plugins.codeowners.backend.config.StatusConfig.KEY_DISABLED_BRANCH;
 
@@ -112,6 +113,11 @@
             input.disabledBranches);
       }
 
+      if (input.fileExtension != null) {
+        codeOwnersConfig.setString(
+            SECTION_CODE_OWNERS, /* subsection= */ null, KEY_FILE_EXTENSION, input.fileExtension);
+      }
+
       validateConfig(projectResource.getProjectState(), codeOwnersConfig);
 
       codeOwnersProjectConfigFile.commit(metaDataUpdate);
diff --git a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/PutCodeOwnerProjectConfigIT.java b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/PutCodeOwnerProjectConfigIT.java
index d864dd9..045f01b 100644
--- a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/PutCodeOwnerProjectConfigIT.java
+++ b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/PutCodeOwnerProjectConfigIT.java
@@ -17,6 +17,7 @@
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.gerrit.server.project.ProjectCache.illegalState;
 import static com.google.gerrit.testing.GerritJUnit.assertThrows;
+import static com.google.gerrit.truth.OptionalSubject.assertThat;
 
 import com.google.common.collect.ImmutableList;
 import com.google.gerrit.acceptance.UseClockStep;
@@ -171,6 +172,23 @@
   }
 
   @Test
+  public void setFileExtension() throws Exception {
+    assertThat(codeOwnersPluginConfiguration.getFileExtension(project)).isEmpty();
+
+    CodeOwnerProjectConfigInput input = new CodeOwnerProjectConfigInput();
+    input.fileExtension = "foo";
+    CodeOwnerProjectConfigInfo updatedConfig =
+        projectCodeOwnersApiFactory.project(project).updateConfig(input);
+    assertThat(updatedConfig.general.fileExtension).isEqualTo("foo");
+    assertThat(codeOwnersPluginConfiguration.getFileExtension(project)).value().isEqualTo("foo");
+
+    input.fileExtension = "";
+    updatedConfig = projectCodeOwnersApiFactory.project(project).updateConfig(input);
+    assertThat(updatedConfig.general.fileExtension).isNull();
+    assertThat(codeOwnersPluginConfiguration.getFileExtension(project)).isEmpty();
+  }
+
+  @Test
   @UseClockStep
   public void checkCommitData() throws Exception {
     RevCommit head1 = projectOperations.project(project).getHead(RefNames.REFS_CONFIG);
diff --git a/resources/Documentation/rest-api.md b/resources/Documentation/rest-api.md
index 32fc803..ebf1afc 100644
--- a/resources/Documentation/rest-api.md
+++ b/resources/Documentation/rest-api.md
@@ -836,6 +836,7 @@
 | ---------- | -------- | ----------- |
 | `disabled` | optional | Whether the code owners functionality should be disabled/enabled for the project.
 | `disabled_branch` | optional | List of branches for which the code owners functionality is disabled. Can be exact refs, ref patterns or regular expressions. Overrides any existing disabled branch configuration.
+| `file_extension` | optional | The file extension that should be used for code owner config files in this project.
 
 ---