diff --git a/MY-BASIC Quick Reference.pdf b/MY-BASIC Quick Reference.pdf
index 6b7c6ce..b72d6e5 100644
Binary files a/MY-BASIC Quick Reference.pdf and b/MY-BASIC Quick Reference.pdf differ
diff --git a/core/my_basic.h b/core/my_basic.h
index 1c6a5c5..32d2dd4 100755
--- a/core/my_basic.h
+++ b/core/my_basic.h
@@ -556,8 +556,8 @@ typedef int (* mb_func_t)(struct mb_interpreter_t*, void**);
 typedef int (* mb_has_routine_arg_func_t)(struct mb_interpreter_t*, void**, mb_value_t*, unsigned, unsigned*, void*);
 typedef int (* mb_pop_routine_arg_func_t)(struct mb_interpreter_t*, void**, mb_value_t*, unsigned, unsigned*, void*, mb_value_t*);
 typedef int (* mb_routine_func_t)(struct mb_interpreter_t*, void**, mb_value_t*, unsigned, void*, mb_has_routine_arg_func_t, mb_pop_routine_arg_func_t);
-typedef int (* mb_debug_stepped_handler_t)(struct mb_interpreter_t*, void**, char*, int, unsigned short, unsigned short);
-typedef void (* mb_error_handler_t)(struct mb_interpreter_t*, mb_error_e, char*, char*, int, unsigned short, unsigned short, int);
+typedef int (* mb_debug_stepped_handler_t)(struct mb_interpreter_t*, void**, const char*, int, unsigned short, unsigned short);
+typedef void (* mb_error_handler_t)(struct mb_interpreter_t*, mb_error_e, const char*, const char*, int, unsigned short, unsigned short, int);
 typedef int (* mb_print_func_t)(const char*, ...);
 typedef int (* mb_input_func_t)(const char*, char*, int);
 typedef int (* mb_import_handler_t)(struct mb_interpreter_t*, const char*);
diff --git a/shell/main.c b/shell/main.c
index 208cd3f..7b1748e 100755
--- a/shell/main.c
+++ b/shell/main.c
@@ -1439,7 +1439,7 @@ static int beep(struct mb_interpreter_t* s, void** l) {
 ** Callbacks and handlers
 */
 
-static int _on_stepped(struct mb_interpreter_t* s, void** l, char* f, int p, unsigned short row, unsigned short col) {
+static int _on_stepped(struct mb_interpreter_t* s, void** l, const char* f, int p, unsigned short row, unsigned short col) {
 	mb_unrefvar(s);
 	mb_unrefvar(l);
 	mb_unrefvar(f);
@@ -1450,7 +1450,7 @@ static int _on_stepped(struct mb_interpreter_t* s, void** l, char* f, int p, uns
 	return MB_FUNC_OK;
 }
 
-static void _on_error(struct mb_interpreter_t* s, mb_error_e e, char* m, char* f, int p, unsigned short row, unsigned short col, int abort_code) {
+static void _on_error(struct mb_interpreter_t* s, mb_error_e e, const char* m, const char* f, int p, unsigned short row, unsigned short col, int abort_code) {
 	mb_unrefvar(s);
 	mb_unrefvar(p);