diff --git a/programs/test/benchmark.c b/programs/test/benchmark.c
index 6313c522a..1ad2034d4 100644
--- a/programs/test/benchmark.c
+++ b/programs/test/benchmark.c
@@ -398,7 +398,7 @@ static unsigned long mbedtls_timing_hardclock( void )
     }
 
     gettimeofday( &tv_cur, NULL );
-    return( ( tv_cur.tv_sec  - tv_init.tv_sec  ) * 1000000
+    return( ( tv_cur.tv_sec  - tv_init.tv_sec  ) * 1000000U
           + ( tv_cur.tv_usec - tv_init.tv_usec ) );
 }
 #endif /* !HAVE_HARDCLOCK */