diff --git a/meson.build b/meson.build
index 1824b0d8c4..5d1d329611 100644
--- a/meson.build
+++ b/meson.build
@@ -325,7 +325,7 @@ else
       get_option('libdir'), 'gio/modules'))
     core_conf.set_quoted('GIO_LIBDIR', join_paths(get_option('prefix'),
       get_option('libdir')))
-    core_conf.set_quoted('GIO_PREFIX', get_option('prefix'))
+    core_conf.set_quoted('GIO_PREFIX', join_paths(get_option('prefix')))
 endif
 
 configinc = include_directories('.')