diff --git a/src/matrix-api.c b/src/matrix-api.c
index ec494e8..9799e7b 100644
--- a/src/matrix-api.c
+++ b/src/matrix-api.c
@@ -390,7 +390,7 @@ matrix_api_media_thumbnail(MatrixAPI *api,
  *             @callback
  * @content_type: (allow-none): the content type of the file being
  *                uploaded
- * @content: the content to be uploaded
+ * @content: (transfer full): the content to be uploaded
  * @error: return location for a #GError, or %NULL
  *
  * Upload some content to the content repository.
@@ -400,7 +400,7 @@ matrix_api_media_upload(MatrixAPI *api,
                         MatrixAPICallback callback,
                         gpointer user_data,
                         const gchar *content_type,
-                        const GByteArray *content,
+                        GByteArray *content,
                         GError **error)
 {
     g_return_if_fail(MATRIX_IS_API(api));
diff --git a/src/matrix-api.h b/src/matrix-api.h
index c37e296..a40c11c 100644
--- a/src/matrix-api.h
+++ b/src/matrix-api.h
@@ -82,7 +82,7 @@ struct _MatrixAPIInterface {
                          MatrixAPICallback callback,
                          gpointer user_data,
                          const gchar *content_type,
-                         const GByteArray *content,
+                         GByteArray *content,
                          GError **error);
 
     /* Presence */
@@ -499,7 +499,7 @@ void matrix_api_media_upload(MatrixAPI *api,
                              MatrixAPICallback callback,
                              gpointer user_data,
                              const gchar *content_type,
-                             const GByteArray *content,
+                             GByteArray *content,
                              GError **error);
 
 /* Presence */