diff --git a/src/assembler.cc b/src/assembler.cc
index d0a8aa4..689e0c8 100644
--- a/src/assembler.cc
+++ b/src/assembler.cc
@@ -61,7 +61,7 @@
 
   // Verify internal state.
   CHECK_EQ(Capacity(), kInitialBufferCapacity);
-  CHECK_EQ(Size(), 0);
+  CHECK_EQ(Size(), 0U);
 }