diff --git a/openbsc/include/openbsc/debug.h b/openbsc/include/openbsc/debug.h
index f99ce60..089132e 100644
--- a/openbsc/include/openbsc/debug.h
+++ b/openbsc/include/openbsc/debug.h
@@ -30,7 +30,7 @@
 
 #define static_assert(exp, name) typedef int dummy##name [(exp) ? 1 : -1];
 
-char *hexdump(unsigned char *buf, int len);
+char *hexdump(const unsigned char *buf, int len);
 void debugp(unsigned int subsys, char *file, int line, int cont, const char *format, ...);
 void debug_parse_category_mask(const char* mask);
 void debug_use_color(int use_color);
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;