diff --git a/include/stk.h b/include/stk.h
index 5309b87f..ad3f6c56 100644
--- a/include/stk.h
+++ b/include/stk.h
@@ -63,7 +63,7 @@ void ofono_stk_set_data(struct ofono_stk *stk, void *data);
 void *ofono_stk_get_data(struct ofono_stk *stk);
 
 void ofono_stk_proactive_command_notify(struct ofono_stk *stk,
-					int length, const guint8 *pdu);
+					int length, const unsigned char *pdu);
 
 #ifdef __cplusplus
 }
diff --git a/src/stk.c b/src/stk.c
index 74b6b347..195725c9 100644
--- a/src/stk.c
+++ b/src/stk.c
@@ -81,7 +81,7 @@ void __ofono_cbs_sim_download(struct ofono_stk *stk,
 }
 
 void ofono_stk_proactive_command_notify(struct ofono_stk *stk,
-		int length, const guint8 *pdu)
+					int length, const unsigned char *pdu)
 {
 	struct stk_command *cmd;
 	char *buf;