diff --git a/src/libstrongswan/plugins/cmac/cmac.c b/src/libstrongswan/plugins/cmac/cmac.c
index c8cb7fbf2..4f222ff4e 100644
--- a/src/libstrongswan/plugins/cmac/cmac.c
+++ b/src/libstrongswan/plugins/cmac/cmac.c
@@ -247,6 +247,9 @@ METHOD(mac_t, set_key, bool,
 {
 	chunk_t resized, iv, l;
 
+	memset(this->t, 0, this->b);
+	this->remaining_bytes = 0;
+
 	/* we support variable keys as defined in RFC 4615 */
 	if (key.len == this->b)
 	{