diff --git a/Modules/FindPkgConfig.cmake b/Modules/FindPkgConfig.cmake
index 547bc520da..ab8af3e604 100644
--- a/Modules/FindPkgConfig.cmake
+++ b/Modules/FindPkgConfig.cmake
@@ -429,7 +429,7 @@ macro(_pkg_set_path_internal)
   else()
     unset(_pkgconfig_allow_system_libs_old)
   endif()
-  set(ENV{PKG_CONFIG_ALLOW_SYSTEM_LIBS} 0)
+  set(ENV{PKG_CONFIG_ALLOW_SYSTEM_LIBS} 1)
 endmacro()
 
 macro(_pkg_restore_path_internal)
@@ -440,6 +440,8 @@ macro(_pkg_restore_path_internal)
   if(DEFINED _pkgconfig_allow_system_libs_old)
     set(ENV{PKG_CONFIG_ALLOW_SYSTEM_LIBS} "${_pkgconfig_allow_system_libs_old}")
     unset(_pkgconfig_allow_system_libs_old)
+  else()
+    unset(ENV{PKG_CONFIG_ALLOW_SYSTEM_LIBS})
   endif()
 
   unset(_extra_paths)