diff --git a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerBackend.java b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerBackend.java
index be5318d..3775f89 100644
--- a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerBackend.java
+++ b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerBackend.java
@@ -112,9 +112,7 @@
    * backend. It this case all {@link CodeOwnerSet}s that have path expressions are ignored and will
    * not have any effect.
    */
-  default Optional<PathExpressionMatcher> getPathExpressionMatcher() {
-    return Optional.empty();
-  }
+  Optional<PathExpressionMatcher> getPathExpressionMatcher();
 
   /**
    * Replaces the old email in the given code owner config file content with the new email.
diff --git a/javatests/com/google/gerrit/plugins/codeowners/backend/config/CodeOwnersPluginConfigurationTest.java b/javatests/com/google/gerrit/plugins/codeowners/backend/config/CodeOwnersPluginConfigurationTest.java
index 25420b5..9883fba 100644
--- a/javatests/com/google/gerrit/plugins/codeowners/backend/config/CodeOwnersPluginConfigurationTest.java
+++ b/javatests/com/google/gerrit/plugins/codeowners/backend/config/CodeOwnersPluginConfigurationTest.java
@@ -39,6 +39,7 @@
 import com.google.gerrit.plugins.codeowners.backend.CodeOwnerConfig;
 import com.google.gerrit.plugins.codeowners.backend.CodeOwnerConfigUpdate;
 import com.google.gerrit.plugins.codeowners.backend.FallbackCodeOwners;
+import com.google.gerrit.plugins.codeowners.backend.PathExpressionMatcher;
 import com.google.gerrit.plugins.codeowners.backend.config.BackendConfig;
 import com.google.gerrit.plugins.codeowners.backend.config.CodeOwnersPluginConfiguration;
 import com.google.gerrit.plugins.codeowners.backend.config.GeneralConfig;
@@ -1083,5 +1084,10 @@
     public Path getFilePath(CodeOwnerConfig.Key codeOwnerConfigKey) {
       throw new UnsupportedOperationException("not implemented");
     }
+
+    @Override
+    public Optional<PathExpressionMatcher> getPathExpressionMatcher() {
+      return Optional.empty();
+    }
   }
 }