diff --git a/src/util/crypto_confirmation.c b/src/util/crypto_confirmation.c
index bbdf701ec..a238d5376 100644
--- a/src/util/crypto_confirmation.c
+++ b/src/util/crypto_confirmation.c
@@ -102,7 +102,7 @@ compute_totp (struct GNUNET_TIME_Timestamp ts,
 
     offset = hmac[sizeof (hmac) - 1] & 0x0f;
     for (int count = 0; count < 4; count++)
-      code |= hmac[offset + 3 - count] << (8 * count);
+      code |= ((uint32_t) hmac[offset + 3 - count]) << (8 * count);
     code &= 0x7fffffff;
     /* always use 8 digits (maximum) */
     code = code % 100000000;