diff --git a/library/timing.c b/library/timing.c
index 6c14a4fd01..ca29e56a66 100644
--- a/library/timing.c
+++ b/library/timing.c
@@ -223,7 +223,7 @@ 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 */