diff --git a/lib/Checker/PthreadLockChecker.cpp b/lib/Checker/PthreadLockChecker.cpp
new file mode 100644
index 0000000..74e266c
--- /dev/null
+++ b/lib/Checker/PthreadLockChecker.cpp
@@ -0,0 +1,141 @@
+//===--- PthreadLockChecker.h - Undefined arguments checker ----*- C++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines PthreadLockChecker, a simple lock -> unlock checker.  Eventually
+// this shouldn't be registered with GRExprEngineInternalChecks.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Checker/PathSensitive/CheckerVisitor.h"
+#include "clang/Checker/BugReporter/BugReporter.h"
+#include "clang/Checker/PathSensitive/GRStateTrait.h"
+#include "GRExprEngineExperimentalChecks.h"
+#include "llvm/ADT/ImmutableSet.h"
+
+using namespace clang;
+
+namespace {
+class PthreadLockChecker
+  : public CheckerVisitor<PthreadLockChecker> {
+  BugType *BT;
+public:
+  PthreadLockChecker() : BT(0) {}
+  static void *getTag() {
+    static int x = 0;
+    return &x;
+  }
+  void PostVisitCallExpr(CheckerContext &C, const CallExpr *CE);
+    
+  void AcquireLock(CheckerContext &C, const CallExpr *CE,
+                   SVal lock, bool isTryLock);
+    
+  void ReleaseLock(CheckerContext &C, const CallExpr *CE,
+                    SVal lock);
+
+};
+} // end anonymous namespace
+
+// GDM Entry for tracking lock state.
+namespace { class LockSet {}; }
+namespace clang {
+template <> struct GRStateTrait<LockSet> :
+  public GRStatePartialTrait<llvm::ImmutableSet<const MemRegion*> > {
+    static void* GDMIndex() { return PthreadLockChecker::getTag(); }
+};
+} // end clang namespace
+
+void clang::RegisterPthreadLockChecker(GRExprEngine &Eng) {
+  Eng.registerCheck(new PthreadLockChecker());
+}
+
+
+void PthreadLockChecker::PostVisitCallExpr(CheckerContext &C,
+                                           const CallExpr *CE) {
+  const GRState *state = C.getState();
+  const Expr *Callee = CE->getCallee();
+  const FunctionTextRegion *R =
+    dyn_cast_or_null<FunctionTextRegion>(state->getSVal(Callee).getAsRegion());
+  
+  if (!R)
+    return;
+  
+  llvm::StringRef FName = R->getDecl()->getName();
+  
+  if (FName == "pthread_mutex_lock") {
+    if (CE->getNumArgs() != 1)
+      return;
+    AcquireLock(C, CE, state->getSVal(CE->getArg(0)), false);
+  }
+  else if (FName == "pthread_mutex_trylock") {
+    if (CE->getNumArgs() != 1)
+      return;
+    AcquireLock(C, CE, state->getSVal(CE->getArg(0)), true);
+  }  
+  else if (FName == "pthread_mutex_unlock") {
+    if (CE->getNumArgs() != 1)
+      return;
+    ReleaseLock(C, CE, state->getSVal(CE->getArg(0)));
+  }
+}
+
+void PthreadLockChecker::AcquireLock(CheckerContext &C, const CallExpr *CE,
+                                     SVal lock, bool isTryLock) {
+  
+  const MemRegion *lockR = lock.getAsRegion();
+  if (!lockR)
+    return;
+  
+  const GRState *state = C.getState();
+  
+  SVal X = state->getSVal(CE);
+  if (X.isUnknownOrUndef())
+    return;
+  
+  DefinedSVal retVal = cast<DefinedSVal>(X);
+  const GRState *lockSucc = state;
+  
+  if (isTryLock) {
+      // Bifurcate the state, and allow a mode where the lock acquisition fails.
+    const GRState *lockFail;
+    llvm::tie(lockFail, lockSucc) = state->Assume(retVal);    
+    assert(lockFail && lockSucc);
+    C.addTransition(C.GenerateNode(CE, lockFail));
+  }
+  else {
+      // Assume that the return value was 0.
+    lockSucc = state->Assume(retVal, false);
+    assert(lockSucc);
+  }
+  
+    // Record that the lock was acquired.  
+  lockSucc = lockSucc->add<LockSet>(lockR);
+  
+  C.addTransition(lockSucc != state ? C.GenerateNode(CE, lockSucc) :
+                  C.getPredecessor());
+}
+
+void PthreadLockChecker::ReleaseLock(CheckerContext &C, const CallExpr *CE,
+                                     SVal lock) {
+
+  const MemRegion *lockR = lock.getAsRegion();
+  if (!lockR)
+    return;
+  
+  const GRState *state = C.getState();
+
+  // Record that the lock was released.  
+  // FIXME: Handle unlocking locks that were never acquired.  This may
+  // require IPA for wrappers.
+  const GRState *unlockState = state->remove<LockSet>(lockR);
+  
+  if (state == unlockState)
+    return;
+  
+  C.addTransition(C.GenerateNode(CE, unlockState));  
+}