diff --git a/lib/CodeGen/StackProtector.cpp b/lib/CodeGen/StackProtector.cpp
index fcaee4208ba..02d8fd6dea9 100644
--- a/lib/CodeGen/StackProtector.cpp
+++ b/lib/CodeGen/StackProtector.cpp
@@ -219,8 +219,8 @@ bool StackProtector::InsertStackProtectors() {
 
     // Split the basic block before the return instruction.
     BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
-    if (DT) {
-      DT->addNewBlock(NewBB, DT->isReachableFromEntry(BB) ? BB : 0);
+    if (DT && DT->isReachableFromEntry(BB)) {
+      DT->addNewBlock(NewBB, BB);
       FailBBDom = DT->findNearestCommonDominator(FailBBDom, BB);
     }
 
@@ -242,7 +242,7 @@ bool StackProtector::InsertStackProtectors() {
   // statements in the function.
   if (!FailBB) return false;
 
-  if (DT)
+  if (DT && FailBBDom)
     DT->addNewBlock(FailBB, FailBBDom);
 
   return true;
diff --git a/test/CodeGen/X86/unreachable-stack-protector.ll b/test/CodeGen/X86/unreachable-stack-protector.ll
new file mode 100644
index 00000000000..eeebceea71d
--- /dev/null
+++ b/test/CodeGen/X86/unreachable-stack-protector.ll
@@ -0,0 +1,19 @@
+; RUN: llc < %s | FileCheck %s
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-apple-darwin10.0.0"
+
+declare i64 @llvm.objectsize.i64(i8*, i1) nounwind readnone
+
+define void @test5() nounwind optsize noinline ssp {
+entry:
+; CHECK: movq ___stack_chk_guard@GOTPCREL(%rip)
+  %buf = alloca [64 x i8], align 16
+  %0 = call i64 @llvm.objectsize.i64(i8* undef, i1 false)
+  br i1 false, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  unreachable
+
+if.end:                                           ; preds = %entry
+  ret void
+}