diff --git a/test/fuzzer/inspector-fuzzer.cc b/test/fuzzer/inspector-fuzzer.cc
index 736195baf5..2a5554396c 100644
--- a/test/fuzzer/inspector-fuzzer.cc
+++ b/test/fuzzer/inspector-fuzzer.cc
@@ -32,13 +32,6 @@ namespace {
 
 base::SmallVector<TaskRunner*, 2> task_runners;
 
-void Terminate() {
-  for (TaskRunner* r : task_runners) {
-    r->Terminate();
-    r->Join();
-  }
-}
-
 class UtilsExtension : public IsolateData::SetupGlobalTask {
  public:
   ~UtilsExtension() override = default;
@@ -88,7 +81,9 @@ class UtilsExtension : public IsolateData::SetupGlobalTask {
   static TaskRunner* backend_runner_;
 
   static void Quit(const v8::FunctionCallbackInfo<v8::Value>& args) {
-    Terminate();
+    // Only terminate, so not join the threads here, since joining concurrently
+    // from multiple threads can be undefined behaviour (see pthread_join).
+    for (TaskRunner* task_runner : task_runners) task_runner->Terminate();
   }
 
   static void CompileAndRunWithOrigin(
@@ -561,7 +556,7 @@ class Watchdog final : public base::Thread {
  private:
   void Run() override {
     if (semaphore_->WaitFor(kMaxExecutionSeconds)) return;
-    Terminate();
+    for (TaskRunner* task_runner : task_runners) task_runner->Terminate();
   }
 
   base::Semaphore* const semaphore_;
diff --git a/test/fuzzer/inspector/empty b/test/fuzzer/inspector/empty
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/test/fuzzer/inspector/foo b/test/fuzzer/inspector/foo
deleted file mode 100644
index 40ca6a920c..0000000000
--- a/test/fuzzer/inspector/foo
+++ /dev/null
@@ -1 +0,0 @@
-smoke test
diff --git a/test/fuzzer/inspector/invalid b/test/fuzzer/inspector/invalid
new file mode 100644
index 0000000000..4476525b2a
--- /dev/null
+++ b/test/fuzzer/inspector/invalid
@@ -0,0 +1 @@
+no valid javascript
diff --git a/test/inspector/inspector-test.cc b/test/inspector/inspector-test.cc
index e33ddca169..b9aa6c6838 100644
--- a/test/inspector/inspector-test.cc
+++ b/test/inspector/inspector-test.cc
@@ -41,13 +41,6 @@ namespace {
 
 base::SmallVector<TaskRunner*, 2> task_runners;
 
-void Terminate() {
-  for (TaskRunner* task_runner : task_runners) {
-    task_runner->Terminate();
-    task_runner->Join();
-  }
-}
-
 class UtilsExtension : public IsolateData::SetupGlobalTask {
  public:
   ~UtilsExtension() override = default;
@@ -154,7 +147,9 @@ class UtilsExtension : public IsolateData::SetupGlobalTask {
   static void Quit(const v8::FunctionCallbackInfo<v8::Value>& args) {
     fflush(stdout);
     fflush(stderr);
-    Terminate();
+    // Only terminate, so not join the threads here, since joining concurrently
+    // from multiple threads can be undefined behaviour (see pthread_join).
+    for (TaskRunner* task_runner : task_runners) task_runner->Terminate();
   }
 
   static void Setlocale(const v8::FunctionCallbackInfo<v8::Value>& args) {