diff --git a/test/acm_random.h b/test/acm_random.h
index a14b671..8b1d51a 100644
--- a/test/acm_random.h
+++ b/test/acm_random.h
@@ -67,7 +67,7 @@
     // Returns a random value near 0 or near 255, to better exercise
     // saturation behavior.
     const uint8_t r = Rand8();
-    return r < 128 ? r << 4 : r >> 4;
+    return static_cast<uint8_t>((r < 128) ? r << 4 : r >> 4);
   }
 
   int PseudoUniform(int range) { return random_.Generate(range); }