diff --git a/src/lib/address_resolve/AddressResolve_DefaultImpl.cpp b/src/lib/address_resolve/AddressResolve_DefaultImpl.cpp
index 9888c96..2fc4e5a 100644
--- a/src/lib/address_resolve/AddressResolve_DefaultImpl.cpp
+++ b/src/lib/address_resolve/AddressResolve_DefaultImpl.cpp
@@ -248,6 +248,10 @@
 
 void Resolver::Shutdown()
 {
+    // mSystemLayer is set in ::Init, so if it's null that means the resolver
+    // has not been initialized or has already been shut down.
+    VerifyOrReturn(mSystemLayer != nullptr);
+
     while (mActiveLookups.begin() != mActiveLookups.end())
     {
         auto current = mActiveLookups.begin();