diff --git a/modules/m_challenge.c b/modules/m_challenge.c
index 5b56cfe4c..68070df7d 100644
--- a/modules/m_challenge.c
+++ b/modules/m_challenge.c
@@ -143,7 +143,8 @@ m_challenge(struct Client *client_p, struct Client *source_p, int parc, const ch
 			return 0;			
 		}
 
-		b_response = rb_base64_decode((const unsigned char *)++parv[1], strlen(parv[1]), &len);
+		parv[1]++;
+		b_response = rb_base64_decode((const unsigned char *)parv[1], strlen(parv[1]), &len);
 
 		if(len != SHA_DIGEST_LENGTH ||
 		   memcmp(source_p->localClient->challenge, b_response, SHA_DIGEST_LENGTH))