diff --git a/cpp/CMakeLists.txt b/cpp/CMakeLists.txt
index 5e916c97..d8e23c85 100644
--- a/cpp/CMakeLists.txt
+++ b/cpp/CMakeLists.txt
@@ -70,6 +70,9 @@ else()
     "Your C++ compiler does NOT support C++11, compiling in C++03 mode." )
 endif()
 
-add_subdirectory( llvm )
+if ( NOT EXTERNAL_LIBCLANG_PATH AND NOT USE_SYSTEM_LIBCLANG )
+  add_subdirectory( llvm )
+endif()
+
 add_subdirectory( BoostParts )
 add_subdirectory( ycm )
diff --git a/cpp/ycm/CMakeLists.txt b/cpp/ycm/CMakeLists.txt
index aadab9ff..153702f7 100644
--- a/cpp/ycm/CMakeLists.txt
+++ b/cpp/ycm/CMakeLists.txt
@@ -33,8 +33,10 @@ include_directories(
   SYSTEM
   ${BoostParts_SOURCE_DIR}
   ${PYTHON_INCLUDE_DIRS}
-  "${LLVM_SOURCE_DIR}/include"
-  "${LLVM_SOURCE_DIR}/tools/clang/include"
+  # We need CMAKE_SOURCE_DIR here instead of LLVM_SOURCE_DIR because the llvm
+  # subdir may not have been included in the build
+  "${CMAKE_SOURCE_DIR}/llvm/include"
+  "${CMAKE_SOURCE_DIR}/llvm/tools/clang/include"
   )
 
 file( GLOB_RECURSE SOURCES *.h *.cpp )