diff --git a/CMakeLists.txt b/CMakeLists.txt
index fe3c8cac..f12cb4f5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -13,6 +13,7 @@ include(KDECompilerSettings)
 include(ECMInstallIcons)
 include(ECMMarkAsTest)
 include(ECMMarkNonGuiExecutable)
+include(ECMOptionalAddSubdirectory)
 include(FeatureSummary)
 include(CheckIncludeFiles)
 
diff --git a/doc/CMakeLists.txt b/doc/CMakeLists.txt
index 65b1626f..cadf8324 100644
--- a/doc/CMakeLists.txt
+++ b/doc/CMakeLists.txt
@@ -1,4 +1,4 @@
-add_subdirectory(khelpcenter)
-add_subdirectory(fundamentals)
-add_subdirectory(glossary)
-add_subdirectory(onlinehelp)
+ecm_optional_add_subdirectory(khelpcenter)
+ecm_optional_add_subdirectory(fundamentals)
+ecm_optional_add_subdirectory(glossary)
+ecm_optional_add_subdirectory(onlinehelp)