diff --git a/src/script_opt/CPP/Compile.h b/src/script_opt/CPP/Compile.h
index 7974c9206a..16f9312b89 100644
--- a/src/script_opt/CPP/Compile.h
+++ b/src/script_opt/CPP/Compile.h
@@ -186,7 +186,7 @@ public:
 	// Returns a mapping of from Attr objects to their associated
 	// initialization information.  The Attr must have previously
 	// been registered.
-	auto ProcessedAttr() { return processed_attr; }
+	auto& ProcessedAttr() { return processed_attr; }
 
 	// True if the given expression is simple enough that we can
 	// generate code to evaluate it directly, and don't need to