diff --git a/plugins/thunderbolt/fu-plugin-thunderbolt.c b/plugins/thunderbolt/fu-plugin-thunderbolt.c
index 19e577dbf..d04e1ea68 100644
--- a/plugins/thunderbolt/fu-plugin-thunderbolt.c
+++ b/plugins/thunderbolt/fu-plugin-thunderbolt.c
@@ -193,19 +193,25 @@ fu_plugin_thunderbolt_udev_get_version (GUdevDevice *udevice)
 static gboolean
 fu_plugin_thunderbolt_is_native (GUdevDevice *udevice, gboolean *is_native, GError **error)
 {
+	gsize nr_chunks;
 	g_autoptr(GFile) nvmem = NULL;
 	g_autoptr(GBytes) controller_fw = NULL;
-	gchar *content;
-	gsize length;
+	g_autoptr(GInputStream) istr = NULL;
 
 	nvmem = fu_plugin_thunderbolt_find_nvmem (udevice, TRUE, error);
 	if (nvmem == NULL)
 		return FALSE;
 
-	if (!g_file_load_contents (nvmem, NULL, &content, &length, NULL, error))
+	/* read just enough bytes to read the status byte */
+	nr_chunks = (FU_TBT_OFFSET_NATIVE + FU_TBT_CHUNK_SZ - 1) / FU_TBT_CHUNK_SZ;
+	istr = G_INPUT_STREAM (g_file_read (nvmem, NULL, error));
+	if (istr == NULL)
+		return FALSE;
+	controller_fw = g_input_stream_read_bytes (istr,
+						   nr_chunks * FU_TBT_CHUNK_SZ,
+						   NULL, error);
+	if (controller_fw == NULL)
 		return FALSE;
-
-	controller_fw = g_bytes_new_take (content, length);
 
 	return fu_thunderbolt_image_controller_is_native (controller_fw,
 							  is_native,
diff --git a/plugins/thunderbolt/fu-thunderbolt-image.c b/plugins/thunderbolt/fu-thunderbolt-image.c
index 40a5951ec..c88aed9b0 100644
--- a/plugins/thunderbolt/fu-thunderbolt-image.c
+++ b/plugins/thunderbolt/fu-thunderbolt-image.c
@@ -787,8 +787,10 @@ fu_thunderbolt_image_controller_is_native (GBytes    *controller_fw,
 	gsize fw_size;
 	const guint8 *fw_data = g_bytes_get_data (controller_fw, &fw_size);
 	const FuThunderboltFwObject controller = { fw_data, fw_size, controller_sections };
-
-	const FuThunderboltFwLocation location = { .offset = 0x7B, .len = 1, .description = "Native", .mask = 0x20 };
-
+	const FuThunderboltFwLocation location = {
+		.offset = FU_TBT_OFFSET_NATIVE,
+		.len = 1,
+		.description = "Native",
+		.mask = 0x20 };
 	return read_bool (&location, &controller, is_native, error);
 }
diff --git a/plugins/thunderbolt/fu-thunderbolt-image.h b/plugins/thunderbolt/fu-thunderbolt-image.h
index f00c42e19..ee7d000ce 100644
--- a/plugins/thunderbolt/fu-thunderbolt-image.h
+++ b/plugins/thunderbolt/fu-thunderbolt-image.h
@@ -15,6 +15,10 @@ typedef enum {
 	UNKNOWN_DEVICE,
 } FuPluginValidation;
 
+/* byte offsets in firmware image */
+#define FU_TBT_OFFSET_NATIVE		0x7B
+#define FU_TBT_CHUNK_SZ			0x40
+
 FuPluginValidation	fu_thunderbolt_image_validate		(GBytes  *controller_fw,
 								 GBytes  *blob_fw,
 								 GError **error);