diff --git a/web/atomic.go b/web/atomic.go
index aab483a..795d8e5 100644
--- a/web/atomic.go
+++ b/web/atomic.go
@@ -1,3 +1,5 @@
+// +build !appengine
+
 package web
 
 import (
diff --git a/web/atomic_appengine.go b/web/atomic_appengine.go
new file mode 100644
index 0000000..027127a
--- /dev/null
+++ b/web/atomic_appengine.go
@@ -0,0 +1,14 @@
+// +build appengine
+
+package web
+
+func (rt *router) getMachine() *routeMachine {
+	rt.lock.Lock()
+	defer rt.lock.Unlock()
+	return rt.machine
+}
+
+// We always hold the lock when calling setMachine.
+func (rt *router) setMachine(m *routeMachine) {
+	rt.machine = m
+}