diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7ffe1065d5c..2ea9a5125e1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -708,3 +708,6 @@ add_tags(ctags
   EXCLUDE_OPTS ${CTAG_EXCLUDES}
   EXCLUDES "*.js" "*.css" ".tox" "python-common/build")
 add_custom_target(tags DEPENDS ctags)
+
+# suppress warning in cmake.eclass
+set(UNUSED_VAR "${CMAKE_INSTALL_LIBDIR}")