diff --git a/lib/fko_encode.c b/lib/fko_encode.c
index c92d421..8eb981c 100644
--- a/lib/fko_encode.c
+++ b/lib/fko_encode.c
@@ -135,7 +135,7 @@ fko_encode_spa_data(fko_ctx_t ctx)
     /* Add the message type value.
     */
     offset = strlen(tbuf);
-    sprintf(((char*)tbuf+offset), ":%i:", ctx->message_type);
+    sprintf(((char*)tbuf+offset), "%i:", ctx->message_type);
 
     /* Add the base64-encoded SPA message.
     */