diff --git a/lldb/unittests/Host/MainLoopTest.cpp b/lldb/unittests/Host/MainLoopTest.cpp
--- a/lldb/unittests/Host/MainLoopTest.cpp
+++ b/lldb/unittests/Host/MainLoopTest.cpp
@@ -174,8 +174,13 @@
 
   auto handle = loop.RegisterSignal(SIGUSR1, make_callback(), error);
   ASSERT_TRUE(error.Success());
-  kill(getpid(), SIGUSR1);
+  std::thread killer([]() {
+    sleep(1);
+    kill(getpid(), SIGUSR1);
+  });
   ASSERT_TRUE(loop.Run().Success());
+  killer.join();
+
   ASSERT_EQ(1u, callback_count);
 }
 
@@ -220,8 +225,12 @@
         SIGUSR1, [&](MainLoopBase &loop) { ++callback2_count; }, error);
     ASSERT_TRUE(error.Success());
 
-    kill(getpid(), SIGUSR1);
+    std::thread killer([]() {
+      sleep(1);
+      kill(getpid(), SIGUSR1);
+    });
     ASSERT_TRUE(loop.Run().Success());
+    killer.join();
     ASSERT_EQ(1u, callback_count);
     ASSERT_EQ(1u, callback2_count);
     ASSERT_EQ(0u, callback3_count);
@@ -233,18 +242,28 @@
         SIGUSR1, [&](MainLoopBase &loop) { ++callback3_count; }, error);
     ASSERT_TRUE(error.Success());
 
-    kill(getpid(), SIGUSR1);
+    std::thread killer([]() {
+      sleep(1);
+      kill(getpid(), SIGUSR1);
+    });
     ASSERT_TRUE(loop.Run().Success());
+    killer.join();
     ASSERT_EQ(2u, callback_count);
     ASSERT_EQ(1u, callback2_count);
     ASSERT_EQ(1u, callback3_count);
   }
 
   // Both extra callbacks should be unregistered now.
-  kill(getpid(), SIGUSR1);
-  ASSERT_TRUE(loop.Run().Success());
-  ASSERT_EQ(3u, callback_count);
-  ASSERT_EQ(1u, callback2_count);
-  ASSERT_EQ(1u, callback3_count);
+  {
+    std::thread killer([]() {
+      sleep(1);
+      kill(getpid(), SIGUSR1);
+    });
+    ASSERT_TRUE(loop.Run().Success());
+    killer.join();
+    ASSERT_EQ(3u, callback_count);
+    ASSERT_EQ(1u, callback2_count);
+    ASSERT_EQ(1u, callback3_count);
+  }
 }
 #endif