diff --git a/test/inspector/inspector-test.cc b/test/inspector/inspector-test.cc
index 6983448d028..a86f5c4e3ca 100644
--- a/test/inspector/inspector-test.cc
+++ b/test/inspector/inspector-test.cc
@@ -565,6 +565,9 @@ class InspectorExtension : public InspectorIsolateData::SetupGlobalTask {
     inspector->Set(isolate, "runNestedMessageLoop",
                    v8::FunctionTemplate::New(
                        isolate, &InspectorExtension::RunNestedMessageLoop));
+    inspector->Set(isolate, "disconnectSession",
+                   v8::FunctionTemplate::New(
+                       isolate, &InspectorExtension::DisconnectSessionSync));
     global->Set(isolate, "inspector", inspector);
   }
 
@@ -853,6 +856,16 @@ class InspectorExtension : public InspectorIsolateData::SetupGlobalTask {
 
     data->task_runner()->RunMessageLoop(true);
   }
+
+  static void DisconnectSessionSync(
+      const v8::FunctionCallbackInfo<v8::Value>& info) {
+    if (info.Length() != 1 || !info[0]->IsInt32()) {
+      FATAL("Internal error: inspector.disconnectSession(session_id).");
+    }
+    v8::Local<v8::Context> context = info.GetIsolate()->GetCurrentContext();
+    InspectorIsolateData* data = InspectorIsolateData::FromContext(context);
+    data->DisconnectSessionSync(info[0].As<v8::Int32>()->Value());
+  }
 };
 
 int InspectorTestMain(int argc, char* argv[]) {
diff --git a/test/inspector/isolate-data.cc b/test/inspector/isolate-data.cc
index 0cc9bb53dce..85e7b4a7405 100644
--- a/test/inspector/isolate-data.cc
+++ b/test/inspector/isolate-data.cc
@@ -226,6 +226,13 @@ std::vector<uint8_t> InspectorIsolateData::DisconnectSession(
   return result;
 }
 
+void InspectorIsolateData::DisconnectSessionSync(int session_id) {
+  auto it = sessions_.find(session_id);
+  if (it == sessions_.end()) return;
+  it->second->Disconnect();
+  sessions_.erase(it);
+}
+
 void InspectorIsolateData::SendMessage(
     int session_id, const v8_inspector::StringView& message) {
   v8::SealHandleScope seal_handle_scope(isolate());
diff --git a/test/inspector/isolate-data.h b/test/inspector/isolate-data.h
index 915afd76464..a201964a822 100644
--- a/test/inspector/isolate-data.h
+++ b/test/inspector/isolate-data.h
@@ -73,6 +73,11 @@ class InspectorIsolateData : public v8_inspector::V8InspectorClient {
       bool is_fully_trusted);
   std::vector<uint8_t> DisconnectSession(int session_id,
                                          TaskRunner* context_task_runner);
+  // Models Blink DevToolsSession::Detach() running synchronously on the
+  // renderer main thread (e.g. from a Mojo disconnect handler dispatched in a
+  // nested message loop). No SealHandleScope so it can be called from inside
+  // re-entrant page JS.
+  void DisconnectSessionSync(int session_id);
   void SendMessage(int session_id, const v8_inspector::StringView& message);
   void BreakProgram(int context_group_id,
                     const v8_inspector::StringView& reason,