diff --git a/src/backdrop.h b/src/backdrop.h
index 8b13789..e018907 100644
--- a/src/backdrop.h
+++ b/src/backdrop.h
@@ -1 +1,7 @@
+#ifndef BACKDROP_H
+#define BACKDROP_H
 
+extern int colour;
+int backdrop (int colour);
+
+#endif