diff --git a/lib/CodeGen/LiveIntervalUnion.cpp b/lib/CodeGen/LiveIntervalUnion.cpp
index d5c7bf0..59d48a4 100644
--- a/lib/CodeGen/LiveIntervalUnion.cpp
+++ b/lib/CodeGen/LiveIntervalUnion.cpp
@@ -168,6 +168,8 @@
       IR.VirtRegI = VirtReg->end();
   }
   findIntersection(FirstInterference);
+  assert((IR.VirtRegI == VirtReg->end() || IR.LiveUnionI.valid())
+         && "Uninitialized iterator");
   return FirstInterference;
 }
 
diff --git a/lib/CodeGen/LiveIntervalUnion.h b/lib/CodeGen/LiveIntervalUnion.h
index 54761c7..5bf86d8 100644
--- a/lib/CodeGen/LiveIntervalUnion.h
+++ b/lib/CodeGen/LiveIntervalUnion.h
@@ -145,8 +145,8 @@
     Query(): LiveUnion(), VirtReg() {}
 
     Query(LiveInterval *VReg, LiveIntervalUnion *LIU):
-      LiveUnion(LIU), VirtReg(VReg), SeenAllInterferences(false),
-      SeenUnspillableVReg(false)
+      LiveUnion(LIU), VirtReg(VReg), CheckedFirstInterference(false),
+      SeenAllInterferences(false), SeenUnspillableVReg(false)
     {}
 
     void clear() {
@@ -159,6 +159,7 @@
     }
 
     void init(LiveInterval *VReg, LiveIntervalUnion *LIU) {
+      assert(VReg && LIU && "Invalid arguments");
       if (VirtReg == VReg && LiveUnion == LIU) {
         // Retain cached results, e.g. firstInterference.
         return;