diff --git a/ament_cmake_core/cmake/core/ament_execute_extensions.cmake b/ament_cmake_core/cmake/core/ament_execute_extensions.cmake
index d5607ed4..2f391517 100644
--- a/ament_cmake_core/cmake/core/ament_execute_extensions.cmake
+++ b/ament_cmake_core/cmake/core/ament_execute_extensions.cmake
@@ -38,10 +38,10 @@ macro(ament_execute_extensions extension_point)
           "name and cmake filename")
       endif()
       list(GET _extension_list 0 _pkg_name)
-      list(GET _extension_list 1 _cmake_filename)
-      if(_pkg_name IN_LIST _ARG_EXCLUDE)
+      if("${_pkg_name}" IN_LIST _ARG_EXCLUDE)
         continue()
       endif()
+      list(GET _extension_list 1 _cmake_filename)
       set(_extension_file "${${_pkg_name}_DIR}/${_cmake_filename}")
       assert_file_exists("${_extension_file}"
         "ament_execute_extensions(${extension_point}) registered extension '${_extension_file}' does not exist")