diff --git a/deps/CMakeLists.txt b/deps/CMakeLists.txt
index 8281e7fb..f6a3b895 100644
--- a/deps/CMakeLists.txt
+++ b/deps/CMakeLists.txt
@@ -48,7 +48,7 @@ else()
 endif()
 
 # -- Cpp2Py --
-if(PythonSupport OR Build_Documentation)
+if(PythonSupport OR (NOT IS_SUBPROJECT AND Build_Documentation))
   external_dependency(Cpp2Py
     GIT_REPO https://github.com/TRIQS/cpp2py
     VERSION 2.0