diff --git a/openbsc/src/gprs/oap_messages.c b/openbsc/src/gprs/oap_messages.c
index 53ea9ac..d81723f 100644
--- a/openbsc/src/gprs/oap_messages.c
+++ b/openbsc/src/gprs/oap_messages.c
@@ -31,8 +31,8 @@
 #include <stdint.h>
 
 
-int osmo_oap_decode(const uint8_t *const_data, size_t data_len,
-		    struct osmo_oap_message *oap_msg)
+int osmo_oap_decode(struct osmo_oap_message *oap_msg,
+		    const uint8_t *const_data, size_t data_len)
 {
 	int rc;
 	uint8_t tag;