diff --git a/test/acm_random.h b/test/acm_random.h
index a29ced2f7..b94b6e195 100644
--- a/test/acm_random.h
+++ b/test/acm_random.h
@@ -35,7 +35,7 @@ class ACMRandom {
   int16_t Rand9Signed(void) {
     // Use 9 bits: values between 255 (0x0FF) and -256 (0x100).
     const uint32_t value = random_.Generate(512);
-    return static_cast<int16_t>(value - 256);
+    return static_cast<int16_t>(value) - 256;
   }
 
   uint8_t Rand8(void) {