--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -76,7 +76,7 @@
 # pkg_check_modules(IBUS REQUIRED ibus-1.0>=1.2.0)
 
 # check doxygen
-find_package(Doxygen REQUIRED)
+find_package(Doxygen)
 
 # =====
 # Define variables
@@ -100,8 +100,7 @@
 # install
 set(MAIN_DOCS
     AUTHORS
-    README
-    INSTALL)
+    README)
 install(FILES ${MAIN_DOCS}
     DESTINATION ${DOCDIR})