diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc b/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc
index f610d15b5a46..e6c5a0bf514a 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc
@@ -457,10 +457,7 @@ void BlockingMutex::Lock() {
 void BlockingMutex::Unlock() {
   atomic_uint32_t *m = reinterpret_cast<atomic_uint32_t *>(&opaque_storage_);
   u32 v = atomic_exchange(m, MtxUnlocked, memory_order_relaxed);
-  if (v == MtxUnlocked) {
-    Printf("FATAL: unlock of unlocked mutex\n");
-    Die();
-  }
+  CHECK_NE(v, MtxUnlocked);
   if (v == MtxSleeping)
     syscall(__NR_futex, m, FUTEX_WAKE_PRIVATE, 1, 0, 0, 0);
 }
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_mac.cc b/compiler-rt/lib/sanitizer_common/sanitizer_mac.cc
index 52e184863cce..c4b8e4c2bcf2 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_mac.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_mac.cc
@@ -30,6 +30,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <libkern/OSAtomic.h>
 
 namespace __sanitizer {
 
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h b/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h
index 15e1caa1b277..56438fce471c 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h
@@ -74,6 +74,7 @@ class BlockingMutex {
   void Unlock();
  private:
   uptr opaque_storage_[10];
+  uptr owner_;  // for debugging
 };
 
 template<typename MutexType>