diff --git a/src/input.c b/src/input.c
index aeed9f3..fbacfce 100644
--- a/src/input.c
+++ b/src/input.c
@@ -886,7 +886,7 @@ void inputchange_macro2_body(char *macro_body)
 	input_now->src.ram_ptr = macro_body;
 }
 // restore input struct from buffer
-void inputchange_back(struct inputchange_buf *icb)
+void inputchange_back(const struct inputchange_buf *icb)
 {
 	input_now = icb->outer_input;
 	GotByte = icb->gb;
diff --git a/src/input.h b/src/input.h
index c80e6eb..36bbe27 100644
--- a/src/input.h
+++ b/src/input.h
@@ -178,7 +178,7 @@ extern void inputchange_macro1_params(struct inputchange_buf *icb, struct locati
 // switch from macro parameters to macro body
 extern void inputchange_macro2_body(char *macro_body);
 // restore input struct from buffer
-extern void inputchange_back(struct inputchange_buf *icb);
+extern void inputchange_back(const struct inputchange_buf *icb);
 
 
 // "include path" stuff: