diff --git a/compiler-rt/lib/hwasan/hwasan_thread.cpp b/compiler-rt/lib/hwasan/hwasan_thread.cpp
--- a/compiler-rt/lib/hwasan/hwasan_thread.cpp
+++ b/compiler-rt/lib/hwasan/hwasan_thread.cpp
@@ -28,6 +28,9 @@
 void Thread::InitRandomState() {
   random_state_ = flags()->random_tags ? RandomSeed() : unique_id_;
 
+  // Now that random_state_ is initialized, we can call GenerateRandomTag().
+  EnableTagging();
+
   // Push a random number of zeros onto the ring buffer so that the first stack
   // tag base will be random.
   for (tag_t i = 0, e = GenerateRandomTag(); i != e; ++i)
@@ -40,6 +43,9 @@
   CHECK_EQ(0, stack_top_);
   CHECK_EQ(0, stack_bottom_);
 
+  // Disable tagging until InitRandomState() is called.
+  DisableTagging();
+
   static u64 unique_id;
   unique_id_ = unique_id++;
   if (auto sz = flags()->heap_history_size)
diff --git a/compiler-rt/test/hwasan/TestCases/pthread_create.c b/compiler-rt/test/hwasan/TestCases/pthread_create.c
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/hwasan/TestCases/pthread_create.c
@@ -0,0 +1,22 @@
+// Tests that our thread initialization hooks work properly with random_tags=1.
+// RUN: %clang_hwasan %s -o %t
+// RUN: %env_hwasan_opts=random_tags=1 %run %t
+// REQUIRES: stable-runtime
+
+#include <pthread.h>
+
+#include <sanitizer/hwasan_interface.h>
+
+volatile int state;
+
+void *Increment(void *arg) {
+  ++state;
+  return NULL;
+}
+
+int main() {
+  __hwasan_enable_allocator_tagging();
+  pthread_t t1;
+  pthread_create(&t1, NULL, Increment, NULL);
+  pthread_join(t1, NULL);
+}
diff --git a/compiler-rt/test/hwasan/TestCases/thread-uaf.c b/compiler-rt/test/hwasan/TestCases/thread-uaf.c
--- a/compiler-rt/test/hwasan/TestCases/thread-uaf.c
+++ b/compiler-rt/test/hwasan/TestCases/thread-uaf.c
@@ -1,8 +1,6 @@
 // Tests UAF detection where Allocate/Deallocate/Use
 // happen in separate threads.
-// RUN: %clang_hwasan %s -o %t && not %run %t > %t.out 2>&1
-// RUN: cat %t.out | FileCheck %s
-// RUN: cat %t.out | FileCheck --check-prefix=CHECK-THREAD %s
+// RUN: %clang_hwasan %s -o %t && not %run %t 2>&1 | FileCheck %s
 // REQUIRES: stable-runtime
 
 #include <pthread.h>
@@ -37,10 +35,10 @@
   // CHECK: in Deallocate
   // CHECK: previously allocated here:
   // CHECK: in Allocate
-  // CHECK-THREAD-DAG: Thread: T2 0x
-  // CHECK-THREAD-DAG: Thread: T3 0x
-  // CHECK-THREAD-DAG: Thread: T0 0x
-  // CHECK-THREAD-DAG: Thread: T1 0x
+  // CHECK-DAG: Thread: T2 0x
+  // CHECK-DAG: Thread: T3 0x
+  // CHECK-DAG: Thread: T0 0x
+  // CHECK-DAG: Thread: T1 0x
   __sync_fetch_and_add(&state, 1);
   return NULL;
 }