diff --git a/llvm/lib/CodeGen/MachineDebugify.cpp b/llvm/lib/CodeGen/MachineDebugify.cpp
--- a/llvm/lib/CodeGen/MachineDebugify.cpp
+++ b/llvm/lib/CodeGen/MachineDebugify.cpp
@@ -153,10 +153,15 @@
       NMD->setOperand(Idx, MDNode::get(Ctx, ValueAsMetadata::getConstant(
                                                 ConstantInt::get(Int32Ty, N))));
     };
+    auto getDebugifyOperand = [&](unsigned Idx) {
+      return mdconst::extract<ConstantInt>(NMD->getOperand(Idx)->getOperand(0))
+          ->getZExtValue();
+    };
     // Set number of lines.
     setDebugifyOperand(0, NextLine - 1);
     // Set number of variables.
-    setDebugifyOperand(1, VarSet.size());
+    auto OldNumVars = getDebugifyOperand(1);
+    setDebugifyOperand(1, OldNumVars + VarSet.size());
   }
 
   return true;