diff --git a/openbsc/src/debug.c b/openbsc/src/debug.c
index 6483710..fa903af 100644
--- a/openbsc/src/debug.c
+++ b/openbsc/src/debug.c
@@ -143,7 +143,7 @@
 
 static char hexd_buff[4096];
 
-char *hexdump(unsigned char *buf, int len)
+char *hexdump(const unsigned char *buf, int len)
 {
 	int i;
 	char *cur = hexd_buff;