diff --git a/src/node_watchdog.cc b/src/node_watchdog.cc
index f9bfa0e0c86f..27c7d83c8a9d 100644
--- a/src/node_watchdog.cc
+++ b/src/node_watchdog.cc
@@ -41,6 +41,7 @@ using v8::Value;
 
 Watchdog::Watchdog(v8::Isolate* isolate, uint64_t ms, bool* timed_out)
     : isolate_(isolate), timed_out_(timed_out) {
+  CHECK_NOT_NULL(timed_out);
 
   int rc;
   rc = uv_loop_init(&loop_);
@@ -103,6 +104,7 @@ void Watchdog::Timer(uv_timer_t* timer) {
 SigintWatchdog::SigintWatchdog(
   v8::Isolate* isolate, bool* received_signal)
     : isolate_(isolate), received_signal_(received_signal) {
+  CHECK_NOT_NULL(received_signal);
   Mutex::ScopedLock lock(SigintWatchdogHelper::GetInstanceActionMutex());
   // Register this watchdog with the global SIGINT/Ctrl+C listener.
   SigintWatchdogHelper::GetInstance()->Register(this);
diff --git a/src/node_watchdog.h b/src/node_watchdog.h
index 096e347d7b3f..a4a31b3a3e9e 100644
--- a/src/node_watchdog.h
+++ b/src/node_watchdog.h
@@ -44,9 +44,7 @@ enum class SignalPropagation {
 
 class Watchdog {
  public:
-  explicit Watchdog(v8::Isolate* isolate,
-                    uint64_t ms,
-                    bool* timed_out = nullptr);
+  explicit Watchdog(v8::Isolate* isolate, uint64_t ms, bool* timed_out);
   ~Watchdog();
   v8::Isolate* isolate() { return isolate_; }
 
@@ -75,8 +73,7 @@ class SigintWatchdogBase {
 
 class SigintWatchdog : public SigintWatchdogBase {
  public:
-  explicit SigintWatchdog(v8::Isolate* isolate,
-                          bool* received_signal = nullptr);
+  explicit SigintWatchdog(v8::Isolate* isolate, bool* received_signal);
   ~SigintWatchdog();
   v8::Isolate* isolate() { return isolate_; }
   SignalPropagation HandleSigint() override;