diff --git a/Utilities/Sphinx/CMakeLists.txt b/Utilities/Sphinx/CMakeLists.txt
index 77a12558a..1baca35e4 100644
--- a/Utilities/Sphinx/CMakeLists.txt
+++ b/Utilities/Sphinx/CMakeLists.txt
@@ -19,6 +19,9 @@ if(NOT CMake_SOURCE_DIR)
   include(${CMake_SOURCE_DIR}/Source/CMakeInstallDestinations.cmake)
   unset(CMAKE_DATA_DIR)
   unset(CMAKE_DATA_DIR CACHE)
+  macro(CMake_OPTIONAL_COMPONENT)
+    set(COMPONENT "")
+  endmacro()
 endif()
 project(CMakeHelp NONE)