diff --git a/misc.c b/misc.c
index 0d5673b3..f3a0eedd 100644
--- a/misc.c
+++ b/misc.c
@@ -814,7 +814,7 @@ void safefree(void *ptr)
 #ifdef DEBUG
 extern void dputs(char *);             /* defined in per-platform *misc.c */
 
-void debug_printf(char *fmt, ...)
+void debug_printf(const char *fmt, ...)
 {
     char *buf;
     va_list ap;
@@ -827,10 +827,10 @@ void debug_printf(char *fmt, ...)
 }
 
 
-void debug_memdump(void *buf, int len, int L)
+void debug_memdump(const void *buf, int len, int L)
 {
     int i;
-    unsigned char *p = buf;
+    const unsigned char *p = buf;
     char foo[17];
     if (L) {
 	int delta;
diff --git a/misc.h b/misc.h
index 2c60748c..4c6bd7ff 100644
--- a/misc.h
+++ b/misc.h
@@ -109,8 +109,8 @@ int match_ssh_id(int stringlen, const void *string, const char *id);
  */
 
 #ifdef DEBUG
-void debug_printf(char *fmt, ...);
-void debug_memdump(void *buf, int len, int L);
+void debug_printf(const char *fmt, ...);
+void debug_memdump(const void *buf, int len, int L);
 #define debug(x) (debug_printf x)
 #define dmemdump(buf,len) debug_memdump (buf, len, 0);
 #define dmemdumpl(buf,len) debug_memdump (buf, len, 1);