diff --git a/CMakeLists.txt b/CMakeLists.txt
index ed2dd7aa..9dd2bfa2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -145,7 +145,7 @@ if(PythonSupport)
 endif()
 
 # Docs
-if(Build_Documentation)
+if(NOT IS_SUBPROJECT AND Build_Documentation)
   add_subdirectory(doc)
 endif()