diff --git a/content/browser/child_process_security_policy_impl.cc b/content/browser/child_process_security_policy_impl.cc
index 0b547de..aa05fdb 100644
--- a/content/browser/child_process_security_policy_impl.cc
+++ b/content/browser/child_process_security_policy_impl.cc
@@ -1150,20 +1150,19 @@
 
   base::AutoLock lock(lock_);
   auto state = security_state_.find(child_id);
-  if (state == security_state_.end()) {
-    // TODO(nick): Returning true instead of false here is a temporary
-    // workaround for https://crbug.com/600441
-    return true;
-  }
-  bool can_access =
-      state->second->CanAccessDataForOrigin(expected_process_lock);
+  bool is_valid_child_id = state != security_state_.end();
+  bool can_access = is_valid_child_id && state->second->CanAccessDataForOrigin(
+                                             expected_process_lock);
   if (!can_access) {
     // Returning false here will result in a renderer kill.  Set some crash
     // keys that will help understand the circumstances of that kill.
     base::debug::SetCrashKeyString(bad_message::GetRequestedSiteURLKey(),
                                    expected_process_lock.spec());
+
     base::debug::SetCrashKeyString(bad_message::GetKilledProcessOriginLockKey(),
-                                   state->second->origin_lock().spec());
+                                   is_valid_child_id
+                                       ? state->second->origin_lock().spec()
+                                       : "(child id not found)");
 
     static auto* requested_origin_key = base::debug::AllocateCrashKeyString(
         "requested_origin", base::debug::CrashKeySize::Size64);
diff --git a/content/browser/dom_storage/session_storage_context_mojo_unittest.cc b/content/browser/dom_storage/session_storage_context_mojo_unittest.cc
index c701b61..ebf479c 100644
--- a/content/browser/dom_storage/session_storage_context_mojo_unittest.cc
+++ b/content/browser/dom_storage/session_storage_context_mojo_unittest.cc
@@ -17,6 +17,7 @@
 #include "base/test/bind_test_util.h"
 #include "base/test/scoped_feature_list.h"
 #include "components/services/leveldb/public/cpp/util.h"
+#include "content/browser/child_process_security_policy_impl.h"
 #include "content/browser/dom_storage/session_storage_database.h"
 #include "content/browser/dom_storage/test/fake_leveldb_database_error_on_write.h"
 #include "content/browser/dom_storage/test/fake_leveldb_service.h"
@@ -62,9 +63,13 @@
     features_.InitAndEnableFeature(blink::features::kOnionSoupDOMStorage);
     mojo::core::SetDefaultProcessErrorCallback(base::BindRepeating(
         &SessionStorageContextMojoTest::OnBadMessage, base::Unretained(this)));
+
+    ChildProcessSecurityPolicyImpl::GetInstance()->Add(kTestProcessId);
   }
 
   void TearDown() override {
+    ChildProcessSecurityPolicyImpl::GetInstance()->Remove(kTestProcessId);
+
     mojo::core::SetDefaultProcessErrorCallback(
         mojo::core::ProcessErrorCallback());
   }