diff --git a/src/ruc/meta/types.h b/src/ruc/meta/types.h
index d342710..efcd0cb 100644
--- a/src/ruc/meta/types.h
+++ b/src/ruc/meta/types.h
@@ -23,3 +23,7 @@ inline bool is(U* input)
 {
 	return input && is<T>(*input);
 }
+
+// References:
+// - serenity/AK/TypeCasts.h
+// - serenity/Userland/Libraries/LibJS/AST.h
diff --git a/src/ruc/system.cpp b/src/ruc/system.cpp
index 300690e..d4120ef 100644
--- a/src/ruc/system.cpp
+++ b/src/ruc/system.cpp
@@ -1,3 +1,4 @@
+#include <algorithm>  // std::sort, std::unique
 #include <cerrno>     // errno, EAGAIN, EINTR
 #include <cstddef>    // size_t
 #include <cstdio>     // perror, ssize_t