diff --git a/libcxx/.clang-format b/libcxx/.clang-format
--- a/libcxx/.clang-format
+++ b/libcxx/.clang-format
@@ -11,6 +11,9 @@
 SortIncludes: false
 ReflowComments: false
 
+# libc++'s preferred indentions of preprocessor statements.
+IndentPPDirectives: AfterHash
+
 # libc++ has some long names so we need more than the 80 column limit imposed by LLVM style, for sensible formatting
 ColumnLimit: 120
 ---