diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
index 07dcc0e4f13..e7ab2f00396 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
@@ -528,8 +528,16 @@ EmitSchedule(DenseMap<MachineBasicBlock*, MachineBasicBlock*> *EM) {
       if (!MI)
         continue;
       MachineBasicBlock *MIBB = MI->getParent();
+#ifndef NDEBUG
+      unsigned LastDIOrder = 0;
+#endif
       for (; DI != DE &&
              (*DI)->getOrder() >= LastOrder && (*DI)->getOrder() < Order; ++DI) {
+#ifndef NDEBUG
+        assert((*DI)->getOrder() >= LastDIOrder &&
+               "SDDbgValue nodes must be in source order!");
+        LastDIOrder = (*DI)->getOrder();
+#endif
         if ((*DI)->isInvalidated())
           continue;
         MachineInstr *DbgMI = Emitter.EmitDbgValue(*DI, MIBB, VRBaseMap, EM);