diff --git a/src/templates_hdf5/templator_hdf5.org b/src/templates_hdf5/templator_hdf5.org
index 7da1889..f119ec7 100644
--- a/src/templates_hdf5/templator_hdf5.org
+++ b/src/templates_hdf5/templator_hdf5.org
@@ -123,7 +123,7 @@ trexio_exit_code trexio_hdf5_init(trexio_t* const file) {
       f->$group$_group = H5Gcreate(f->file_id, $GROUP$_GROUP_NAME, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
       break;
   }
-  assert (f->$group$_group > 0L);
+  if (f->$group$_group <= 0L) return TREXIO_INVALID_ID;
 
   return TREXIO_SUCCESS;
 }
diff --git a/src/templates_text/templator_text.org b/src/templates_text/templator_text.org
index 103a330..aa00eec 100644
--- a/src/templates_text/templator_text.org
+++ b/src/templates_text/templator_text.org
@@ -441,7 +441,7 @@ trexio_exit_code trexio_text_flush_$group$(trexio_text_t* const file) {
   if ($group$->to_flush == 0) return TREXIO_SUCCESS;
 
   FILE* f = $group$->file;
-  assert (f != NULL);
+  if (f == NULL) return TREXIO_INVALID_ARG_1;
   fseek(f, 0L, SEEK_SET);
 
   /* Write the dimensioning variables */