diff --git a/services/web/test/unit/bootstrap.js b/services/web/test/unit/bootstrap.js
index 8d254a2691..2bdf4744a4 100644
--- a/services/web/test/unit/bootstrap.js
+++ b/services/web/test/unit/bootstrap.js
@@ -52,3 +52,17 @@ LIBRARIES.forEach(lib => {
 SandboxedModule.configure({
   requires: GLOBAL_REQUIRE_CACHE_FOR_SANDBOXED_MODULES
 })
+
+// sandboxed-module somehow registers every fake module it creates in this
+// module's children array, which uses quite a big amount of memory. We'll take
+// a copy of the module children array and restore it after each test so that
+// the garbage collector has a chance to reclaim the fake modules.
+let initialModuleChildren
+before('record initial module children', function() {
+  initialModuleChildren = module.children.slice()
+})
+
+afterEach('restore module children', function() {
+  // Delete leaking sandboxed modules
+  module.children = initialModuleChildren.slice()
+})