diff --git a/samples/pdfium_test.cc b/samples/pdfium_test.cc
index a91e132..d5bf3c0 100644
--- a/samples/pdfium_test.cc
+++ b/samples/pdfium_test.cc
@@ -582,6 +582,9 @@
   v8::Platform* platform = v8::platform::CreateDefaultPlatform();
   v8::V8::InitializePlatform(platform);
   v8::V8::Initialize();
+  // By enabling predicatble mode, V8 won't post any background tasks.
+  const char predictable_flag[] = "--predictable";
+  v8::V8::SetFlagsFromString(predictable_flag, strlen(predictable_flag));
 
 #ifdef V8_USE_EXTERNAL_STARTUP_DATA
   v8::StartupData natives;
diff --git a/testing/embedder_test.cpp b/testing/embedder_test.cpp
index 9b21609..70c32af 100644
--- a/testing/embedder_test.cpp
+++ b/testing/embedder_test.cpp
@@ -193,6 +193,9 @@
 
 void EmbedderTest::SetUp() {
     v8::V8::InitializeICU();
+    // By enabling predicatble mode, V8 won't post any background tasks.
+    const char predictable_flag[] = "--predictable";
+    v8::V8::SetFlagsFromString(predictable_flag, strlen(predictable_flag));
 
 #ifdef V8_USE_EXTERNAL_STARTUP_DATA
     ASSERT_TRUE(GetExternalData(g_exe_path_, "natives_blob.bin", &natives_));