diff --git a/mlir/lib/Dialect/Transform/TuneExtension/TuneExtensionOps.cpp b/mlir/lib/Dialect/Transform/TuneExtension/TuneExtensionOps.cpp
index f727118f3f9a0..2bd6205c69341 100644
--- a/mlir/lib/Dialect/Transform/TuneExtension/TuneExtensionOps.cpp
+++ b/mlir/lib/Dialect/Transform/TuneExtension/TuneExtensionOps.cpp
@@ -156,7 +156,7 @@ DiagnosedSilenceableFailure
 transform::tune::AlternativesOp::apply(transform::TransformRewriter &rewriter,
                                        transform::TransformResults &results,
                                        transform::TransformState &state) {
-  std::optional<size_t> selectedRegionIdx;
+  std::optional<int64_t> selectedRegionIdx;
 
   if (auto selectedRegionAttr = getSelectedRegionAttr())
     selectedRegionIdx = selectedRegionAttr->getSExtValue();
@@ -232,7 +232,7 @@ LogicalResult transform::tune::AlternativesOp::verify() {
   }
 
   if (auto selectedRegionAttr = getSelectedRegionAttr()) {
-    size_t regionIdx = selectedRegionAttr->getSExtValue();
+    int64_t regionIdx = selectedRegionAttr->getSExtValue();
     if (regionIdx < 0 || regionIdx >= getNumRegions())
       return emitOpError()
              << "'selected_region' attribute specifies region at index "