diff --git a/lib/Checker/CMakeLists.txt b/lib/Checker/CMakeLists.txt
index 7b21d08..0e95b08 100644
--- a/lib/Checker/CMakeLists.txt
+++ b/lib/Checker/CMakeLists.txt
@@ -62,6 +62,7 @@
   UndefResultChecker.cpp
   UndefinedArraySubscriptChecker.cpp
   UndefinedAssignmentChecker.cpp
+  UnixAPIChecker.cpp
   VLASizeChecker.cpp
   ValueManager.cpp
   )
diff --git a/lib/Checker/GRExprEngine.cpp b/lib/Checker/GRExprEngine.cpp
index 7f86319..3872856 100644
--- a/lib/Checker/GRExprEngine.cpp
+++ b/lib/Checker/GRExprEngine.cpp
@@ -318,6 +318,7 @@
   RegisterNoReturnFunctionChecker(Eng);
   RegisterBuiltinFunctionChecker(Eng);
   RegisterOSAtomicChecker(Eng);
+  RegisterUnixAPIChecker(Eng);
 }
 
 GRExprEngine::GRExprEngine(AnalysisManager &mgr, GRTransferFuncs *tf)
diff --git a/lib/Checker/GRExprEngineInternalChecks.h b/lib/Checker/GRExprEngineInternalChecks.h
index 9877626..a4bcd72 100644
--- a/lib/Checker/GRExprEngineInternalChecks.h
+++ b/lib/Checker/GRExprEngineInternalChecks.h
@@ -44,6 +44,7 @@
 
 // API checks.
 void RegisterOSAtomicChecker(GRExprEngine &Eng);
+void RegisterUnixAPIChecker(GRExprEngine &Eng);
 
 } // end clang namespace
 #endif
diff --git a/lib/Checker/UnixAPIChecker.cpp b/lib/Checker/UnixAPIChecker.cpp
new file mode 100644
index 0000000..b80f784
--- /dev/null
+++ b/lib/Checker/UnixAPIChecker.cpp
@@ -0,0 +1,151 @@
+//= UnixAPIChecker.h - Checks preconditions for various Unix APIs --*- C++ -*-//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines UnixAPIChecker, which is an assortment of checks on calls
+// to various, widely used UNIX/Posix functions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Checker/PathSensitive/CheckerVisitor.h"
+#include "clang/Checker/BugReporter/BugReporter.h"
+#include "clang/Checker/PathSensitive/GRStateTrait.h"
+#include "llvm/ADT/StringSwitch.h"
+#include "GRExprEngineInternalChecks.h"
+#include <fcntl.h>
+
+using namespace clang;
+
+namespace {
+class UnixAPIChecker : public CheckerVisitor<UnixAPIChecker> {
+  enum SubChecks {
+    OpenFn = 0,
+    NumChecks
+  };
+
+  BugType *BTypes[NumChecks];
+
+public:
+  UnixAPIChecker() { memset(BTypes, 0, sizeof(*BTypes) * NumChecks); }
+  static void *getTag() { static unsigned tag = 0; return &tag; }
+
+  void PreVisitCallExpr(CheckerContext &C, const CallExpr *CE);
+};
+} //end anonymous namespace
+
+void clang::RegisterUnixAPIChecker(GRExprEngine &Eng) {
+  Eng.registerCheck(new UnixAPIChecker());
+}
+
+//===----------------------------------------------------------------------===//
+// Utility functions.
+//===----------------------------------------------------------------------===//
+
+static inline void LazyInitialize(BugType *&BT, const char *name) {
+  if (BT)
+    return;
+  BT = new BugType(name, "Unix API");
+}
+
+//===----------------------------------------------------------------------===//
+// "open" (man 2 open)
+//===----------------------------------------------------------------------===//
+
+static void CheckOpen(CheckerContext &C, const CallExpr *CE, BugType *&BT) {
+  LazyInitialize(BT, "Improper use of 'open'");
+
+  // Look at the 'oflags' argument for the O_CREAT flag.
+  const GRState *state = C.getState();
+
+  if (CE->getNumArgs() < 2) {
+    // The frontend should issue a warning for this case, so this is a sanity
+    // check.
+    return;
+  }
+
+  // Now check if oflags has O_CREAT set.
+  const Expr *oflagsEx = CE->getArg(1);
+  const SVal V = state->getSVal(oflagsEx);
+  if (!isa<NonLoc>(V)) {
+    // The case where 'V' can be a location can only be due to a bad header,
+    // so in this case bail out.
+    return;
+  }
+  NonLoc oflags = cast<NonLoc>(V);
+  NonLoc ocreateFlag =
+    cast<NonLoc>(C.getValueManager().makeIntVal((uint64_t) O_CREAT,
+                                                oflagsEx->getType()));
+  SVal maskedFlagsUC = C.getSValuator().EvalBinOpNN(state, BinaryOperator::And,
+                                                    oflags, ocreateFlag,
+                                                    oflagsEx->getType());
+  if (maskedFlagsUC.isUnknownOrUndef())
+    return;
+  DefinedSVal maskedFlags = cast<DefinedSVal>(maskedFlagsUC);
+
+  // Check if maskedFlags is non-zero.
+  const GRState *trueState, *falseState;
+  llvm::tie(trueState, falseState) = state->Assume(maskedFlags);
+
+  // Only emit an error if the value of 'maskedFlags' is properly
+  // constrained;
+  if (!(trueState && !falseState))
+    return;
+
+  if (CE->getNumArgs() < 3) {
+    ExplodedNode *N = C.GenerateSink(trueState);
+    EnhancedBugReport *report =
+      new EnhancedBugReport(*BT,
+                            "Call to 'open' requires a third argument when "
+                            "the 'O_CREAT' flag is set", N);
+    report->addRange(oflagsEx->getSourceRange());
+    C.EmitReport(report);
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// Central dispatch function.
+//===----------------------------------------------------------------------===//
+
+typedef void (*SubChecker)(CheckerContext &C, const CallExpr *CE, BugType *&BT);
+namespace {
+  class SubCheck {
+    SubChecker SC;
+    BugType **BT;
+  public:
+    SubCheck(SubChecker sc, BugType *& bt) : SC(sc), BT(&bt) {}
+    SubCheck() : SC(NULL), BT(NULL) {}
+
+    void run(CheckerContext &C, const CallExpr *CE) const {
+      if (SC)
+        SC(C, CE, *BT);
+    }
+  };
+} // end anonymous namespace
+
+void UnixAPIChecker::PreVisitCallExpr(CheckerContext &C, const CallExpr *CE) {
+  // Get the callee.  All the functions we care about are C functions
+  // with simple identifiers.
+  const GRState *state = C.getState();
+  const Expr *Callee = CE->getCallee();
+  const FunctionTextRegion *Fn =
+    dyn_cast_or_null<FunctionTextRegion>(state->getSVal(Callee).getAsRegion());
+
+  if (!Fn)
+    return;
+
+  const IdentifierInfo *FI = Fn->getDecl()->getIdentifier();
+  if (!FI)
+    return;
+
+  const SubCheck &SC =
+    llvm::StringSwitch<SubCheck>(FI->getName())
+      .Case("open", SubCheck(CheckOpen, BTypes[OpenFn]))
+      .Default(SubCheck());
+
+  SC.run(C, CE);
+}