diff --git a/libc/include/CMakeLists.txt b/libc/include/CMakeLists.txt
index 039b86a3b10c16..d9cb5b97c05406 100644
--- a/libc/include/CMakeLists.txt
+++ b/libc/include/CMakeLists.txt
@@ -209,6 +209,7 @@ add_gen_header(
     .llvm-libc-types.struct_timespec
     .llvm-libc-types.struct_timeval
     .llvm-libc-types.clockid_t
+    .llvm-libc-types.size_t
 )
 
 add_gen_header(
diff --git a/libc/include/time.h.def b/libc/include/time.h.def
index 2355e8822fad7a..3b748a7edd1497 100644
--- a/libc/include/time.h.def
+++ b/libc/include/time.h.def
@@ -11,6 +11,7 @@
 
 #include "__llvm-libc-common.h"
 #include "llvm-libc-macros/time-macros.h"
+#include "llvm-libc-types/size_t.h"
 
 %%public_api()