diff --git a/CMLibCotire.cmake b/CMLibCotire.cmake
index 8d5b68a..af483ce 100644
--- a/CMLibCotire.cmake
+++ b/CMLibCotire.cmake
@@ -1,4 +1,4 @@
-include(cotire)
+include(cotire OPTIONAL)
 
 if(COMMAND cotire)
   option(CMLIB_COTIRE_ENABLE_PRECOMPILED_HEADER "Enable precompiled headers" OFF)
diff --git a/thirdparty/cotire.cmake b/thirdparty/cotire.cmake
index 18b55d8..2f970ca 100644
--- a/thirdparty/cotire.cmake
+++ b/thirdparty/cotire.cmake
@@ -640,6 +640,7 @@ function (cotire_get_target_include_directories _config _language _target _inclu
 	endforeach()
 	list (REMOVE_DUPLICATES _includeDirs)
 	list (REMOVE_DUPLICATES _systemIncludeDirs)
+	list (REMOVE_ITEM _systemIncludeDirs "/usr/include")
 	if (CMAKE_${_language}_IMPLICIT_INCLUDE_DIRECTORIES)
 		list (REMOVE_ITEM _includeDirs ${CMAKE_${_language}_IMPLICIT_INCLUDE_DIRECTORIES})
 	endif()