diff --git a/library/debug.c b/library/debug.c
index 843b9f5..33151db 100644
--- a/library/debug.c
+++ b/library/debug.c
@@ -52,8 +52,8 @@
     return( str );
 }
 
-void debug_print_msg( ssl_context *ssl, int level,
-                      char *file, int line, char *text )
+void debug_print_msg( const ssl_context *ssl, int level,
+                      const char *file, int line, const char *text )
 {
     char str[512];
     int maxlen = sizeof( str ) - 1;
@@ -66,8 +66,9 @@
     ssl->f_dbg( ssl->p_dbg, level, str );
 }
 
-void debug_print_ret( ssl_context *ssl, int level,
-                      char *file, int line, char *text, int ret )
+void debug_print_ret( const ssl_context *ssl, int level,
+                      const char *file, int line,
+                      const char *text, int ret )
 {
     char str[512];
     int maxlen = sizeof( str ) - 1;
@@ -82,8 +83,8 @@
     ssl->f_dbg( ssl->p_dbg, level, str );
 }
 
-void debug_print_buf( ssl_context *ssl, int level,
-                      char *file, int line, char *text,
+void debug_print_buf( const ssl_context *ssl, int level,
+                      const char *file, int line, const char *text,
                       unsigned char *buf, int len )
 {
     char str[512];
@@ -124,8 +125,9 @@
         ssl->f_dbg( ssl->p_dbg, level, "\n" );
 }
 
-void debug_print_mpi( ssl_context *ssl, int level,
-                      char *file, int line, char *text, mpi *X )
+void debug_print_mpi( const ssl_context *ssl, int level,
+                      const char *file, int line,
+                      const char *text, const mpi *X )
 {
     char str[512];
     int i, j, k, n, maxlen = sizeof( str ) - 1;
@@ -169,8 +171,9 @@
     ssl->f_dbg( ssl->p_dbg, level, "\n" );
 }
 
-void debug_print_crt( ssl_context *ssl, int level,
-                      char *file, int line, char *text, x509_cert *crt )
+void debug_print_crt( const ssl_context *ssl, int level,
+                      const char *file, int line,
+                      const char *text, const x509_cert *crt )
 {
     char str[1024], prefix[64];
     int i = 0, maxlen = sizeof( prefix ) - 1;