diff --git a/src/main/java/com/android/tools/r8/dex/DexOutputBuffer.java b/src/main/java/com/android/tools/r8/dex/DexOutputBuffer.java
index 2d1da51..69f1e34 100644
--- a/src/main/java/com/android/tools/r8/dex/DexOutputBuffer.java
+++ b/src/main/java/com/android/tools/r8/dex/DexOutputBuffer.java
@@ -35,6 +35,7 @@
   }
 
   private void ensureSpaceFor(int bytes) {
+    assert bytes >= 0;
     if (byteBuffer.remaining() < bytes) {
       int newSize = byteBuffer.capacity() + Math.max(byteBuffer.capacity(), bytes * 2);
       CompatByteBuffer newBuffer = allocateByteBuffer(newSize);