diff --git a/c_glib/arrow-glib/reader.cpp b/c_glib/arrow-glib/reader.cpp
index a21b3756167..ba835fd33a6 100644
--- a/c_glib/arrow-glib/reader.cpp
+++ b/c_glib/arrow-glib/reader.cpp
@@ -243,8 +243,8 @@ garrow_record_batch_stream_reader_new(GArrowInputStream *stream,
   auto arrow_input_stream = garrow_input_stream_get_raw(stream);
   std::shared_ptr<BaseType> arrow_reader;
   auto status = ReaderType::Open(arrow_input_stream, &arrow_reader);
-  auto subtype = std::dynamic_pointer_cast<ReaderType>(arrow_reader);
   if (garrow_error_check(error, status, "[record-batch-stream-reader][open]")) {
+    auto subtype = std::dynamic_pointer_cast<ReaderType>(arrow_reader);
     return garrow_record_batch_stream_reader_new_raw(&subtype);
   } else {
     return NULL;
diff --git a/c_glib/arrow-glib/writer.cpp b/c_glib/arrow-glib/writer.cpp
index c08db19987e..7d3b59457fd 100644
--- a/c_glib/arrow-glib/writer.cpp
+++ b/c_glib/arrow-glib/writer.cpp
@@ -223,8 +223,8 @@ garrow_record_batch_stream_writer_new(GArrowOutputStream *sink,
   auto status = WriterType::Open(arrow_sink,
                                  garrow_schema_get_raw(schema),
                                  &arrow_writer);
-  auto subtype = std::dynamic_pointer_cast<WriterType>(arrow_writer);
   if (garrow_error_check(error, status, "[record-batch-stream-writer][open]")) {
+    auto subtype = std::dynamic_pointer_cast<WriterType>(arrow_writer);
     return garrow_record_batch_stream_writer_new_raw(&subtype);
   } else {
     return NULL;
@@ -270,8 +270,8 @@ garrow_record_batch_file_writer_new(GArrowOutputStream *sink,
   auto status = WriterType::Open(arrow_sink.get(),
                                  garrow_schema_get_raw(schema),
                                  &arrow_writer);
-  auto subtype = std::dynamic_pointer_cast<WriterType>(arrow_writer);
   if (garrow_error_check(error, status, "[record-batch-file-writer][open]")) {
+    auto subtype = std::dynamic_pointer_cast<WriterType>(arrow_writer);
     return garrow_record_batch_file_writer_new_raw(&subtype);
   } else {
     return NULL;