diff --git a/system_state.h b/system_state.h
index 6f06a34..313d670 100644
--- a/system_state.h
+++ b/system_state.h
@@ -17,6 +17,7 @@
 // SystemState is the root class within the update engine. So we should avoid
 // any circular references in header file inclusion. Hence forward-declaring
 // the required classes.
+class ClockInterface;
 class ConnectionManager;
 class PrefsInterface;
 class PayloadStateInterface;
@@ -43,6 +44,9 @@
   virtual void set_device_policy(const policy::DevicePolicy* device_policy) = 0;
   virtual const policy::DevicePolicy* device_policy() const = 0;
 
+  // Gets the interface object for the clock.
+  virtual ClockInterface* clock() = 0;
+
   // Gets the connection manager object.
   virtual ConnectionManager* connection_manager() = 0;