diff --git a/lib/Checker/UndefinedArraySubscriptChecker.cpp b/lib/Checker/UndefinedArraySubscriptChecker.cpp
new file mode 100644
index 0000000..a2792ad
--- /dev/null
+++ b/lib/Checker/UndefinedArraySubscriptChecker.cpp
@@ -0,0 +1,56 @@
+//===--- UndefinedArraySubscriptChecker.h ----------------------*- C++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines UndefinedArraySubscriptChecker, a builtin check in GRExprEngine
+// that performs checks for undefined array subscripts.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Checker/PathSensitive/CheckerVisitor.h"
+#include "clang/Checker/BugReporter/BugReporter.h"
+#include "GRExprEngineInternalChecks.h"
+
+using namespace clang;
+
+namespace {
+class UndefinedArraySubscriptChecker
+  : public CheckerVisitor<UndefinedArraySubscriptChecker> {
+  BugType *BT;
+public:
+  UndefinedArraySubscriptChecker() : BT(0) {}
+  static void *getTag() {
+    static int x = 0;
+    return &x;
+  }
+  void PreVisitArraySubscriptExpr(CheckerContext &C, 
+                                  const ArraySubscriptExpr *A);
+};
+} // end anonymous namespace
+
+void clang::RegisterUndefinedArraySubscriptChecker(GRExprEngine &Eng) {
+  Eng.registerCheck(new UndefinedArraySubscriptChecker());
+}
+
+void 
+UndefinedArraySubscriptChecker::PreVisitArraySubscriptExpr(CheckerContext &C, 
+                                                const ArraySubscriptExpr *A) {
+  if (C.getState()->getSVal(A->getIdx()).isUndef()) {
+    if (ExplodedNode *N = C.GenerateSink()) {
+      if (!BT)
+        BT = new BuiltinBug("Array subscript is undefined");
+
+      // Generate a report for this bug.
+      EnhancedBugReport *R = new EnhancedBugReport(*BT, BT->getName(), N);
+      R->addRange(A->getIdx()->getSourceRange());
+      R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, 
+                           A->getIdx());
+      C.EmitReport(R);
+    }
+  }
+}