diff --git a/subsys/bluetooth/host/at.h b/subsys/bluetooth/host/at.h
index ae2c7f95d80..ea19319f33f 100644
--- a/subsys/bluetooth/host/at.h
+++ b/subsys/bluetooth/host/at.h
@@ -89,7 +89,7 @@ typedef int (*handle_cmd_input_t)(struct at_client *at, struct net_buf *buf,
 				  enum at_cmd_type type);
 
 struct at_client {
-	char *buf;
+	unsigned char *buf;
 	uint8_t pos;
 	uint8_t buf_max_len;
 	uint8_t state;