diff --git a/libc/CMakeLists.txt b/libc/CMakeLists.txt
index 414be906336bf..0cec6fc07d982 100644
--- a/libc/CMakeLists.txt
+++ b/libc/CMakeLists.txt
@@ -7,11 +7,6 @@ endif()
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
-# `llvm-project/llvm/CMakeLists.txt` adds the following directive
-# `include_directories( ${LLVM_INCLUDE_DIR} ${LLVM_MAIN_INCLUDE_DIR})`
-# We undo it to be able to precisely control what is getting included.
-set_directory_properties(PROPERTIES INCLUDE_DIRECTORIES "")
-
 # Default to C++17
 set(CMAKE_CXX_STANDARD 17)
 
diff --git a/libc/cmake/modules/LLVMLibCObjectRules.cmake b/libc/cmake/modules/LLVMLibCObjectRules.cmake
index c10b81f1af8cb..994437f55d274 100644
--- a/libc/cmake/modules/LLVMLibCObjectRules.cmake
+++ b/libc/cmake/modules/LLVMLibCObjectRules.cmake
@@ -151,6 +151,7 @@ function(_build_gpu_objects fq_target_name internal_target_name)
     ${ARGN}
   )
 
+  set(include_dirs ${LIBC_SOURCE_DIR} ${LIBC_INCLUDE_DIR})
   set(common_compile_options ${ADD_GPU_OBJ_COMPILE_OPTIONS})
   if(NOT ADD_GPU_OBJ_CXX_STANDARD)
     set(ADD_GPU_OBJ_CXX_STANDARD ${CMAKE_CXX_STANDARD})
@@ -188,10 +189,13 @@ function(_build_gpu_objects fq_target_name internal_target_name)
       )
 
       target_compile_options(${gpu_target_name} PRIVATE ${compile_options})
-      target_include_directories(${gpu_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-      target_include_directories(${gpu_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+      target_include_directories(${gpu_target_name} PRIVATE ${include_dirs})
       target_compile_definitions(${gpu_target_name} PRIVATE LIBC_COPT_PUBLIC_PACKAGING)
-      set_target_properties(${gpu_target_name} PROPERTIES CXX_STANDARD ${ADD_GPU_OBJ_CXX_STANDARD})
+      set_target_properties(
+        ${gpu_target_name}
+        PROPERTIES
+          CXX_STANDARD ${ADD_GPU_OBJ_CXX_STANDARD}
+      )
       if(ADD_GPU_OBJ_DEPENDS)
         add_dependencies(${gpu_target_name} ${ADD_GPU_OBJ_DEPENDS})
       endif()
@@ -257,8 +261,7 @@ function(_build_gpu_objects fq_target_name internal_target_name)
     target_compile_options(${fq_target_name} PRIVATE
                            "SHELL:-Xclang -fembed-offload-object=${packaged_gpu_binary}")
   endforeach()
-  target_include_directories(${fq_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-  target_include_directories(${fq_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+  target_include_directories(${fq_target_name} PRIVATE ${include_dirs})
   add_dependencies(${fq_target_name}
                    ${full_deps_list} ${packaged_gpu_names} ${stub_target_name})
 
@@ -282,8 +285,7 @@ function(_build_gpu_objects fq_target_name internal_target_name)
       get_nvptx_compile_options(nvptx_options ${LIBC_GPU_TARGET_ARCHITECTURE})
       target_compile_options(${internal_target_name} PRIVATE ${nvptx_options})
     endif()
-    target_include_directories(${internal_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-    target_include_directories(${internal_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+    target_include_directories(${internal_target_name} PRIVATE ${include_dirs})
     if(full_deps_list)
       add_dependencies(${internal_target_name} ${full_deps_list})
     endif()
@@ -367,8 +369,12 @@ function(create_object_library fq_target_name)
       ${ADD_OBJECT_SRCS}
       ${ADD_OBJECT_HDRS}
     )
-    target_include_directories(${fq_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-    target_include_directories(${fq_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+    target_include_directories(
+      ${fq_target_name}
+      PRIVATE
+        ${LIBC_SOURCE_DIR}
+        ${LIBC_INCLUDE_DIR}
+    )
     target_compile_options(${fq_target_name} PRIVATE ${compile_options})
   endif()
 
@@ -627,6 +633,7 @@ function(create_entrypoint_object fq_target_name)
     "${ADD_ENTRYPOINT_OBJ_FLAGS}"
     ${ADD_ENTRYPOINT_OBJ_COMPILE_OPTIONS}
   )
+  set(include_dirs ${LIBC_SOURCE_DIR} ${LIBC_INCLUDE_DIR})
   get_fq_deps_list(fq_deps_list ${ADD_ENTRYPOINT_OBJ_DEPENDS})
   set(full_deps_list ${fq_deps_list} libc.src.__support.common)
 
@@ -663,8 +670,7 @@ function(create_entrypoint_object fq_target_name)
       ${ADD_ENTRYPOINT_OBJ_HDRS}
     )
     target_compile_options(${internal_target_name} BEFORE PRIVATE ${common_compile_options})
-    target_include_directories(${internal_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-    target_include_directories(${internal_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+    target_include_directories(${internal_target_name} PRIVATE ${include_dirs})
     add_dependencies(${internal_target_name} ${full_deps_list})
     target_link_libraries(${internal_target_name} ${full_deps_list})
 
@@ -678,8 +684,7 @@ function(create_entrypoint_object fq_target_name)
       ${ADD_ENTRYPOINT_OBJ_HDRS}
     )
     target_compile_options(${fq_target_name} BEFORE PRIVATE ${common_compile_options} -DLIBC_COPT_PUBLIC_PACKAGING)
-    target_include_directories(${fq_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-    target_include_directories(${fq_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+    target_include_directories(${fq_target_name} PRIVATE ${include_dirs})
     add_dependencies(${fq_target_name} ${full_deps_list})
     target_link_libraries(${fq_target_name} ${full_deps_list})
   endif()
diff --git a/libc/cmake/modules/LLVMLibCTestRules.cmake b/libc/cmake/modules/LLVMLibCTestRules.cmake
index 3d02a37e96db5..e1286b4ab9631 100644
--- a/libc/cmake/modules/LLVMLibCTestRules.cmake
+++ b/libc/cmake/modules/LLVMLibCTestRules.cmake
@@ -148,8 +148,12 @@ function(create_libc_unittest fq_target_name)
     ${LIBC_UNITTEST_SRCS}
     ${LIBC_UNITTEST_HDRS}
   )
-  target_include_directories(${fq_build_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-  target_include_directories(${fq_build_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+  target_include_directories(
+    ${fq_build_target_name}
+    PRIVATE
+      ${LIBC_SOURCE_DIR}
+      ${LIBC_INCLUDE_DIR}
+  )
   target_compile_options(
     ${fq_build_target_name}
     PRIVATE -fpie ${LIBC_COMPILE_OPTIONS_DEFAULT}
@@ -382,8 +386,12 @@ function(add_libc_fuzzer target_name)
     ${LIBC_FUZZER_SRCS}
     ${LIBC_FUZZER_HDRS}
   )
-  target_include_directories(${fq_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-  target_include_directories(${fq_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+  target_include_directories(
+    ${fq_target_name}
+    PRIVATE
+      ${LIBC_SOURCE_DIR}
+      ${LIBC_INCLUDE_DIR}
+  )
 
   target_link_libraries(${fq_target_name} PRIVATE 
     ${link_object_files} 
@@ -508,8 +516,12 @@ function(add_integration_test test_name)
   )
   set_target_properties(${fq_build_target_name}
       PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
-  target_include_directories(${fq_build_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-  target_include_directories(${fq_build_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+  target_include_directories(
+    ${fq_build_target_name}
+    PRIVATE
+      ${LIBC_SOURCE_DIR}
+      ${LIBC_INCLUDE_DIR}
+  )
   target_compile_options(${fq_build_target_name}
       PRIVATE -fpie -ffreestanding -fno-exceptions -fno-rtti ${INTEGRATION_TEST_COMPILE_OPTIONS})
   # The GPU build requires overriding the default CMake triple and architecture.
@@ -671,8 +683,12 @@ function(add_libc_hermetic_test test_name)
       RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
       #OUTPUT_NAME ${fq_target_name}
   )
-  target_include_directories(${fq_build_target_name} SYSTEM PRIVATE ${LIBC_INCLUDE_DIR})
-  target_include_directories(${fq_build_target_name} PRIVATE ${LIBC_SOURCE_DIR})
+  target_include_directories(
+    ${fq_build_target_name}
+    PRIVATE
+      ${LIBC_SOURCE_DIR}
+      ${LIBC_INCLUDE_DIR}
+  )
   target_compile_options(${fq_build_target_name}
       PRIVATE ${LIBC_HERMETIC_TEST_COMPILE_OPTIONS} ${HERMETIC_TEST_COMPILE_OPTIONS})
 
diff --git a/libc/utils/HdrGen/CMakeLists.txt b/libc/utils/HdrGen/CMakeLists.txt
index 0ec1cba542d40..0b1612e8a886a 100644
--- a/libc/utils/HdrGen/CMakeLists.txt
+++ b/libc/utils/HdrGen/CMakeLists.txt
@@ -14,7 +14,7 @@ add_tablegen(libc-hdrgen LIBC
   PublicAPICommand.h
 )
 
-target_include_directories(libc-hdrgen PRIVATE ${LLVM_INCLUDE_DIR} ${LLVM_MAIN_INCLUDE_DIR})
+target_include_directories(libc-hdrgen PRIVATE ${LIBC_SOURCE_DIR})
 target_link_libraries(libc-hdrgen PRIVATE LibcTableGenUtil)
 
 add_subdirectory(PrototypeTestGen)
diff --git a/libc/utils/LibcTableGenUtil/CMakeLists.txt b/libc/utils/LibcTableGenUtil/CMakeLists.txt
index dca6a7bb83065..222f177ee2f77 100644
--- a/libc/utils/LibcTableGenUtil/CMakeLists.txt
+++ b/libc/utils/LibcTableGenUtil/CMakeLists.txt
@@ -6,4 +6,3 @@ add_llvm_library(
   LINK_COMPONENTS Support TableGen
 )
 target_include_directories(LibcTableGenUtil PUBLIC ${LIBC_SOURCE_DIR})
-target_include_directories(LibcTableGenUtil PRIVATE ${LLVM_INCLUDE_DIR} ${LLVM_MAIN_INCLUDE_DIR})