diff --git a/src/pages.c b/src/pages.c
index 2c3643fb..ecfe66ab 100644
--- a/src/pages.c
+++ b/src/pages.c
@@ -1482,7 +1482,7 @@ byte Delete_layer(T_List_of_pages *list, int layer)
 
 
 /// Merges the current layer onto the one below it.
-byte Merge_layer()
+byte Merge_layer(void)
 {
   int i;
   for (i=0; i<Main.image_width*Main.image_height; i++)
diff --git a/src/pages.h b/src/pages.h
index 8bf05464..827bf384 100644
--- a/src/pages.h
+++ b/src/pages.h
@@ -58,7 +58,7 @@ byte Add_layer(T_List_of_pages *list, int layer);
 /// Delete a layer from the latest page of a list. Returns 0 on success.
 byte Delete_layer(T_List_of_pages *list, int layer);
 /// Merges the current layer onto the one below it.
-byte Merge_layer();
+byte Merge_layer(void);
 /// Backs up a layer, unless it's already different from previous history step.
 int Dup_layer_if_shared(T_Page * page, int layer);