diff --git a/libc/utils/HdrGen/CMakeLists.txt b/libc/utils/HdrGen/CMakeLists.txt
--- a/libc/utils/HdrGen/CMakeLists.txt
+++ b/libc/utils/HdrGen/CMakeLists.txt
@@ -1,3 +1,5 @@
+include(TableGen)
+
 set(LLVM_LINK_COMPONENTS Support)
 
 add_tablegen(libc-hdrgen LIBC