diff --git a/include/llvm/Support/CallSite.h b/include/llvm/Support/CallSite.h
index 4f4ae965e32..fab3b7c8962 100644
--- a/include/llvm/Support/CallSite.h
+++ b/include/llvm/Support/CallSite.h
@@ -83,6 +83,10 @@ public:
       return I->op_begin()+3; // Skip Function, BB, BB
   }
   arg_iterator arg_end() const { return I->op_end(); }
+
+  bool operator<(const CallSite &CS) const {
+    return getInstruction() < CS.getInstruction();
+  }
 };
 
 #endif