diff --git a/third-party/unittest/UnitTestMain/TestMain.cpp b/third-party/unittest/UnitTestMain/TestMain.cpp
--- a/third-party/unittest/UnitTestMain/TestMain.cpp
+++ b/third-party/unittest/UnitTestMain/TestMain.cpp
@@ -29,6 +29,10 @@
                                             true /* Disable crash reporting */);
   }
 
+  // Use the "threadsafe" test style for death tests -- the "fast" test style
+  // can cause deadlocks.
+  testing::GTEST_FLAG(death_test_style) = "threadsafe";
+
   // Initialize both gmock and gtest.
   testing::InitGoogleMock(&argc, argv);