diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 681bf9c..6de602e 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3073,7 +3073,12 @@
   Value *Sub = SI->getCondition();
   if (!Offset->isNullValue())
     Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
-  Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
+  Value *Cmp;
+  // If NumCases overflowed, then all possible values jump to the successor.
+  if (NumCases->isNullValue() && SI->getNumCases() != 0)
+    Cmp = ConstantInt::getTrue(SI->getContext());
+  else
+    Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
   BranchInst *NewBI = Builder.CreateCondBr(
       Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
 
diff --git a/test/Transforms/SimplifyCFG/switch-to-icmp.ll b/test/Transforms/SimplifyCFG/switch-to-icmp.ll
index 414f847..e9a6db4 100644
--- a/test/Transforms/SimplifyCFG/switch-to-icmp.ll
+++ b/test/Transforms/SimplifyCFG/switch-to-icmp.ll
@@ -37,3 +37,21 @@
 ; CHECK: @test2
 ; CHECK: %switch = icmp ult i32 %x, 2
 }
+
+define i32 @test3(i1 %flag) {
+entry:
+ switch i1 %flag, label %bad [
+   i1 true, label %good
+   i1 false, label %good
+ ]
+
+good:
+ ret i32 0
+
+bad:
+ ret i32 1
+
+; CHECK: @test3
+; CHECK: entry:
+; CHECK-NEXT: ret i32 0
+}