diff --git a/src/LarvaDatasets.jl b/src/LarvaDatasets.jl
index c63d4a07de11bb79804c41d468b83168c92ad939..1e90013cc052a01c7711fed0a314f5e4520bc92f 100644
--- a/src/LarvaDatasets.jl
+++ b/src/LarvaDatasets.jl
@@ -706,7 +706,7 @@ function new_write_larva_dataset_hdf5(output_dir, input_data;
             # ensure labels are ordered as provided in input;
             # see https://gitlab.pasteur.fr/nyx/TaggingBackends/-/issues/24
             if labels isa AbstractDict
-                labels = collect(keys(labels))
+                labels = string.(keys(labels))
             end
             h5["labels"] = labels
             h5["label_counts"] = [get(classcounts, Symbol(label), 0) for label in labels]