diff --git a/flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp b/flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp
index 4cf39716a7375..746c275f37eac 100644
--- a/flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp
+++ b/flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp
@@ -209,6 +209,7 @@ class BoxedProcedurePass
       BoxprocTypeRewriter typeConverter(mlir::UnknownLoc::get(context));
       mlir::Dialect *firDialect = context->getLoadedDialect("fir");
       getModule().walk([&](mlir::Operation *op) {
+        bool opIsValid = true;
         typeConverter.setLocation(op->getLoc());
         if (auto addr = mlir::dyn_cast<BoxAddrOp>(op)) {
           mlir::Type ty = addr.getVal().getType();
@@ -220,6 +221,7 @@ class BoxedProcedurePass
             rewriter.setInsertionPoint(addr);
             rewriter.replaceOpWithNewOp<ConvertOp>(
                 addr, typeConverter.convertType(addr.getType()), addr.getVal());
+            opIsValid = false;
           } else if (typeConverter.needsConversion(resTy)) {
             rewriter.startOpModification(op);
             op->getResult(0).setType(typeConverter.convertType(resTy));
@@ -271,10 +273,12 @@ class BoxedProcedurePass
                 llvm::ArrayRef<mlir::Value>{tramp});
             rewriter.replaceOpWithNewOp<ConvertOp>(embox, toTy,
                                                    adjustCall.getResult(0));
+            opIsValid = false;
           } else {
             // Just forward the function as a pointer.
             rewriter.replaceOpWithNewOp<ConvertOp>(embox, toTy,
                                                    embox.getFunc());
+            opIsValid = false;
           }
         } else if (auto global = mlir::dyn_cast<GlobalOp>(op)) {
           auto ty = global.getType();
@@ -297,6 +301,7 @@ class BoxedProcedurePass
             rewriter.replaceOpWithNewOp<AllocaOp>(
                 mem, toTy, uniqName, bindcName, isPinned, mem.getTypeparams(),
                 mem.getShape());
+            opIsValid = false;
           }
         } else if (auto mem = mlir::dyn_cast<AllocMemOp>(op)) {
           auto ty = mem.getType();
@@ -310,6 +315,7 @@ class BoxedProcedurePass
             rewriter.replaceOpWithNewOp<AllocMemOp>(
                 mem, toTy, uniqName, bindcName, mem.getTypeparams(),
                 mem.getShape());
+            opIsValid = false;
           }
         } else if (auto coor = mlir::dyn_cast<CoordinateOp>(op)) {
           auto ty = coor.getType();
@@ -321,6 +327,7 @@ class BoxedProcedurePass
             auto toBaseTy = typeConverter.convertType(baseTy);
             rewriter.replaceOpWithNewOp<CoordinateOp>(coor, toTy, coor.getRef(),
                                                       coor.getCoor(), toBaseTy);
+            opIsValid = false;
           }
         } else if (auto index = mlir::dyn_cast<FieldIndexOp>(op)) {
           auto ty = index.getType();
@@ -332,6 +339,7 @@ class BoxedProcedurePass
             auto toOnTy = typeConverter.convertType(onTy);
             rewriter.replaceOpWithNewOp<FieldIndexOp>(
                 index, toTy, index.getFieldId(), toOnTy, index.getTypeparams());
+            opIsValid = false;
           }
         } else if (auto index = mlir::dyn_cast<LenParamIndexOp>(op)) {
           auto ty = index.getType();
@@ -343,6 +351,7 @@ class BoxedProcedurePass
             auto toOnTy = typeConverter.convertType(onTy);
             rewriter.replaceOpWithNewOp<LenParamIndexOp>(
                 index, toTy, index.getFieldId(), toOnTy, index.getTypeparams());
+            opIsValid = false;
           }
         } else if (op->getDialect() == firDialect) {
           rewriter.startOpModification(op);
@@ -354,7 +363,7 @@ class BoxedProcedurePass
           rewriter.finalizeOpModification(op);
         }
         // Ensure block arguments are updated if needed.
-        if (op->getNumRegions() != 0) {
+        if (opIsValid && op->getNumRegions() != 0) {
           rewriter.startOpModification(op);
           for (mlir::Region &region : op->getRegions())
             for (mlir::Block &block : region.getBlocks())