diff --git a/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index d53bc3f0ccc..8c41c728c06 100644
--- a/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -1116,7 +1116,7 @@ struct VISIBILITY_HIDDEN FFSOpt : public LibCallOptimization {
     Value *F = Intrinsic::getDeclaration(Callee->getParent(),
                                          Intrinsic::cttz, &ArgType, 1);
     Value *V = B.CreateCall(F, Op, "cttz");
-    V = B.CreateAdd(V, ConstantInt::get(Type::Int32Ty, 1), "tmp");
+    V = B.CreateAdd(V, ConstantInt::get(V->getType(), 1), "tmp");
     V = B.CreateIntCast(V, Type::Int32Ty, false, "tmp");
     
     Value *Cond = B.CreateICmpNE(Op, Constant::getNullValue(ArgType), "tmp");
diff --git a/test/Transforms/SimplifyLibCalls/FFS.ll b/test/Transforms/SimplifyLibCalls/FFS.ll
index bdf43ef69f7..d6a504af867 100644
--- a/test/Transforms/SimplifyLibCalls/FFS.ll
+++ b/test/Transforms/SimplifyLibCalls/FFS.ll
@@ -28,3 +28,9 @@ define i32 @main() {
 	ret i32 %rslt5
 }
 
+
+; PR4206
+define i32 @a(i64) nounwind {
+        %2 = call i32 @ffsll(i64 %0)            ; <i32> [#uses=1]
+        ret i32 %2
+}