diff --git a/CMakeLists.txt b/CMakeLists.txt
index 82ce4e62ee..fa8d1e6d63 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -44,6 +44,7 @@ include(KDECMakeSettings)
 include(KDECompilerSettings)
 
 include(ECMInstallIcons)
+include(ECMOptionalAddSubdirectory)
 
 add_definitions(-DQT_DISABLE_DEPRECATED_BEFORE=0)