diff --git a/lib/Transforms/IPO/SimplifyLibCalls.cpp b/lib/Transforms/IPO/SimplifyLibCalls.cpp
index a3be34577f8..8aed1e8103b 100644
--- a/lib/Transforms/IPO/SimplifyLibCalls.cpp
+++ b/lib/Transforms/IPO/SimplifyLibCalls.cpp
@@ -780,7 +780,7 @@ public:
     // do the concatenation for us.
     Value *MemcpyOps[] = {
       Dst, Src,
-      ConstantInt::get(SLC.getIntPtrType(), SrcLen), // length including nul.
+      ConstantInt::get(SLC.getIntPtrType(), SrcLen+1), // length including nul.
       ConstantInt::get(Type::Int32Ty, 1) // alignment
     };
     new CallInst(SLC.get_memcpy(), MemcpyOps, 4, "", CI);