diff --git a/meson.build b/meson.build
index 6a85c35b1f..a75ffa8f42 100644
--- a/meson.build
+++ b/meson.build
@@ -1908,6 +1908,7 @@ if meson.can_run_host_binaries() and have_gobject_introspection
   gimp_run_env.append('GIMP_TESTING_PLUGINDIRS', meson.global_build_root() / 'plug-ins/common/test-plug-ins/')
 
   gimp_run_env.set('GIMP_TESTING_INTERPRETER_DIRS', meson.global_build_root() / 'plug-ins/python/')
+  gimp_run_env.append('GIMP_TESTING_INTERPRETER_DIRS', meson.global_build_root() / 'extensions/')
   gimp_run_env.set('GIMP_TESTING_ENVIRON_DIRS', meson.global_source_root() / 'data/environ/')
 
   gimp_run_env.prepend('GI_TYPELIB_PATH', prefix / 'lib/girepository-1.0/')