diff --git a/llvm/include/llvm/ADT/SCCIterator.h b/llvm/include/llvm/ADT/SCCIterator.h
--- a/llvm/include/llvm/ADT/SCCIterator.h
+++ b/llvm/include/llvm/ADT/SCCIterator.h
@@ -133,9 +133,11 @@
   /// This informs the \c scc_iterator that the specified \c Old node
   /// has been deleted, and \c New is to be used in its place.
   void ReplaceNode(NodeRef Old, NodeRef New) {
-    assert(nodeVisitNumbers.count(Old) && "Old not in scc_iterator?");
-    nodeVisitNumbers[New] = nodeVisitNumbers[Old];
-    nodeVisitNumbers.erase(Old);
+    auto it = nodeVisitNumbers.find(Old);
+    assert(it != nodeVisitNumbers.end() && "Old not in scc_iterator?");
+    unsigned OldVisitNumber = it->second;
+    nodeVisitNumbers.erase(it);
+    nodeVisitNumbers[New] = OldVisitNumber;
   }
 };