diff --git a/src/main/java/com/android/tools/r8/utils/InternalOptions.java b/src/main/java/com/android/tools/r8/utils/InternalOptions.java
index 7b0af95..e35964a 100644
--- a/src/main/java/com/android/tools/r8/utils/InternalOptions.java
+++ b/src/main/java/com/android/tools/r8/utils/InternalOptions.java
@@ -1292,7 +1292,7 @@
     // TODO(b/205611444): Enable by default.
     private boolean enableClassInitializerDeadlockDetection = true;
     private boolean enableInterfaceMerging =
-        System.getProperty("com.android.tools.r8.disableHorizontalInterfaceMerging") == null;
+        System.getProperty("com.android.tools.r8.enableHorizontalInterfaceMerging") != null;
     private boolean enableInterfaceMergingInInitial = false;
     private boolean enableSyntheticMerging = true;
     private boolean ignoreRuntimeTypeChecksForTesting = false;
@@ -1366,6 +1366,10 @@
       enableClassInitializerDeadlockDetection = true;
     }
 
+    public void setEnableInterfaceMerging() {
+      enableInterfaceMerging = true;
+    }
+
     public void setEnableInterfaceMergingInInitial() {
       enableInterfaceMergingInInitial = true;
     }
diff --git a/src/test/java/com/android/tools/r8/TestCompilerBuilder.java b/src/test/java/com/android/tools/r8/TestCompilerBuilder.java
index 3702430..2f419b6 100644
--- a/src/test/java/com/android/tools/r8/TestCompilerBuilder.java
+++ b/src/test/java/com/android/tools/r8/TestCompilerBuilder.java
@@ -55,6 +55,7 @@
         options.testing.allowUnnecessaryDontWarnWildcards = false;
         options.testing.reportUnusedProguardConfigurationRules = true;
         options.horizontalClassMergerOptions().enable();
+        options.horizontalClassMergerOptions().setEnableInterfaceMerging();
       };
 
   final Backend backend;