diff --git a/llvm/lib/CodeGen/VirtRegMap.cpp b/llvm/lib/CodeGen/VirtRegMap.cpp
index ddbb72b..fcba8ad 100644
--- a/llvm/lib/CodeGen/VirtRegMap.cpp
+++ b/llvm/lib/CodeGen/VirtRegMap.cpp
@@ -338,6 +338,7 @@
   assert(LI.liveAt(BaseIndex) &&
          "Reads of completely dead register should be marked undef already");
   unsigned SubRegIdx = MO.getSubReg();
+  assert(SubRegIdx != 0 && LI.hasSubRanges());
   LaneBitmask UseMask = TRI->getSubRegIndexLaneMask(SubRegIdx);
   // See if any of the relevant subregister liveranges is defined at this point.
   for (const LiveInterval::SubRange &SR : LI.subranges()) {