diff --git a/src/runtime/crash_cgo_test.go b/src/runtime/crash_cgo_test.go
index 2e2f95e5f0..2642c28f0d 100644
--- a/src/runtime/crash_cgo_test.go
+++ b/src/runtime/crash_cgo_test.go
@@ -100,9 +100,18 @@ func TestCgoExternalThreadSIGPROF(t *testing.T) {
 		// ppc64 (issue #8912)
 		t.Skipf("no external linking on ppc64")
 	}
-	got := runTestProg(t, "testprogcgo", "CgoExternalThreadSIGPROF")
-	want := "OK\n"
-	if got != want {
+
+	exe, err := buildTestProg(t, "testprogcgo", "-tags=threadprof")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := testEnv(exec.Command(exe, "CgoExternalThreadSIGPROF")).CombinedOutput()
+	if err != nil {
+		t.Fatalf("exit status: %v\n%s", err, got)
+	}
+
+	if want := "OK\n"; string(got) != want {
 		t.Fatalf("expected %q, but got:\n%s", want, got)
 	}
 }
@@ -113,9 +122,19 @@ func TestCgoExternalThreadSignal(t *testing.T) {
 	case "plan9", "windows":
 		t.Skipf("no pthreads on %s", runtime.GOOS)
 	}
-	got := runTestProg(t, "testprogcgo", "CgoExternalThreadSignal")
-	want := "OK\n"
-	if got != want {
+
+	exe, err := buildTestProg(t, "testprogcgo", "-tags=threadprof")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := testEnv(exec.Command(exe, "CgoExternalThreadSIGPROF")).CombinedOutput()
+	if err != nil {
+		t.Fatalf("exit status: %v\n%s", err, got)
+	}
+
+	want := []byte("OK\n")
+	if !bytes.Equal(got, want) {
 		t.Fatalf("expected %q, but got:\n%s", want, got)
 	}
 }
diff --git a/src/runtime/testdata/testprogcgo/threadpprof.go b/src/runtime/testdata/testprogcgo/threadpprof.go
index f057d591c3..81965831a7 100644
--- a/src/runtime/testdata/testprogcgo/threadpprof.go
+++ b/src/runtime/testdata/testprogcgo/threadpprof.go
@@ -53,6 +53,18 @@ void pprofCgoThreadTraceback(void* parg) {
 int getCPUHogThreadCount() {
 	return __sync_add_and_fetch(&cpuHogThreadCount, 0);
 }
+
+static void* cpuHogDriver(void* arg __attribute__ ((unused))) {
+	while (1) {
+		cpuHogThread();
+	}
+	return 0;
+}
+
+void runCPUHogThread() {
+	pthread_t tid;
+	pthread_create(&tid, 0, cpuHogDriver, 0);
+}
 */
 import "C"
 
@@ -84,6 +96,8 @@ func CgoPprofThread() {
 		os.Exit(2)
 	}
 
+	C.runCPUHogThread()
+
 	t0 := time.Now()
 	for C.getCPUHogThreadCount() < 2 && time.Since(t0) < time.Second {
 		time.Sleep(100 * time.Millisecond)
diff --git a/src/runtime/testdata/testprogcgo/threadprof.go b/src/runtime/testdata/testprogcgo/threadprof.go
index 516f8dce9e..2d4c1039fb 100644
--- a/src/runtime/testdata/testprogcgo/threadprof.go
+++ b/src/runtime/testdata/testprogcgo/threadprof.go
@@ -2,7 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// We only build this file with the tag "threadprof", since it starts
+// a thread running a busy loop at constructor time.
+
 // +build !plan9,!windows
+// +build threadprof
 
 package main
 
@@ -21,6 +25,7 @@ static void *thread1(void *p) {
 	spinlock = 0;
 	return NULL;
 }
+
 __attribute__((constructor)) void issue9456() {
 	pthread_t tid;
 	pthread_create(&tid, 0, thread1, NULL);