diff --git a/src/main/java/com/android/tools/r8/dump/DumpOptions.java b/src/main/java/com/android/tools/r8/dump/DumpOptions.java
index c8787e5..8f0e15e 100644
--- a/src/main/java/com/android/tools/r8/dump/DumpOptions.java
+++ b/src/main/java/com/android/tools/r8/dump/DumpOptions.java
@@ -312,7 +312,8 @@
   }
 
   public static class Builder {
-    private Backend backend;
+    // Initialize backend to DEX for backwards compatibility.
+    private Backend backend = Backend.DEX;
     private Tool tool;
     private CompilationMode compilationMode;
     private int minApi;