Index: lib/StaticAnalyzer/Core/CoreEngine.cpp
===================================================================
--- lib/StaticAnalyzer/Core/CoreEngine.cpp
+++ lib/StaticAnalyzer/Core/CoreEngine.cpp
@@ -657,7 +657,17 @@
   HasGeneratedNodes = true;
   bool IsNew;
   ExplodedNode *N = C.Eng.G.getNode(Loc, State, MarkAsSink, &IsNew);
-  N->addPredecessor(FromN, C.Eng.G);
+
+  bool EdgeExists = false;
+  for (auto I = N->pred_begin(), E = N->pred_end(); I != E; ++I)
+    if (*I == FromN) {
+      EdgeExists = true;
+      break;
+    }
+
+  if (!EdgeExists)
+    N->addPredecessor(FromN, C.Eng.G);
+
   Frontier.erase(FromN);
 
   if (!IsNew)
Index: lib/StaticAnalyzer/Core/ExplodedGraph.cpp
===================================================================
--- lib/StaticAnalyzer/Core/ExplodedGraph.cpp
+++ lib/StaticAnalyzer/Core/ExplodedGraph.cpp
@@ -215,6 +215,11 @@
 
 void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) {
   assert (!V->isSink());
+  for (ExplodedNode *N : Preds)
+    assert(N != V && "Edge already exists");
+  for (ExplodedNode *N : V->Succs)
+    assert(N != this && "Edge already exists");
+
   Preds.addNode(V, G);
   V->Succs.addNode(this, G);
 #ifndef NDEBUG