diff --git a/extensions/protobuf/internal/qualify.cc b/extensions/protobuf/internal/qualify.cc
index 7c1503d1c..49de92621 100644
--- a/extensions/protobuf/internal/qualify.cc
+++ b/extensions/protobuf/internal/qualify.cc
@@ -14,6 +14,7 @@
 
 #include "extensions/protobuf/internal/qualify.h"
 
+#include <cstdint>
 #include <string>
 #include <utility>
 
@@ -290,13 +291,13 @@ absl::StatusOr<int> ProtoQualifyState::CheckListIndex(
         cel::builtin::kIndex);
   }
 
-  int index = *qualifier.GetInt64Key();
+  int64_t index = *qualifier.AsInt();
   int size = reflection_->FieldSize(*message_, repeated_field_desc_);
   if (index < 0 || index >= size) {
     return absl::InvalidArgumentError(
         absl::StrCat("index out of bounds: index=", index, " size=", size));
   }
-  return index;
+  return static_cast<int>(index);
 }
 
 absl::Status ProtoQualifyState::ApplyAttributeQualifierList(
diff --git a/extensions/select_optimization_test.cc b/extensions/select_optimization_test.cc
index 227b902e8..7e15dc897 100644
--- a/extensions/select_optimization_test.cc
+++ b/extensions/select_optimization_test.cc
@@ -1301,6 +1301,23 @@ INSTANTIATE_TEST_SUITE_P(
                                    HasSubstr("index out of bounds")));
             },
         },
+        {
+            // -2^32, which would read element 0 if truncated to an int.
+            "select_with_repeated_index_beyond_int32",
+            "nested_test_all_types.payload.repeated_nested_message"
+            "[-4294967296].bb",
+            {{"nested_test_all_types",
+              R"pb(
+                payload { repeated_nested_message {} }
+              )pb"}},
+            ActivationSetupFn(),
+            [](const absl::StatusOr<Value>& got) {
+              ASSERT_OK_AND_ASSIGN(Value result, got);
+              ASSERT_TRUE(result->Is<ErrorValue>()) << result->DebugString();
+              EXPECT_THAT(result.GetError().NativeValue(),
+                          StatusIs(absl::StatusCode::kInvalidArgument));
+            },
+        },
         {
             "unknown_field",
             "((false)? a.child.child : b.child).child.payload.single_int64",