diff --git a/psm_utils/io/idxml.py b/psm_utils/io/idxml.py
index 2bd2e14..c993d85 100644
--- a/psm_utils/io/idxml.py
+++ b/psm_utils/io/idxml.py
@@ -194,7 +194,7 @@ def _parse_psm(
             score=peptide_hit.getScore(),
             precursor_mz=peptide_id.getMZ(),
             retention_time=peptide_id.getRT(),
-            ion_mobility=float(peptide_id.getMetaValue("IM")) if peptide_id.getMetaValue("IM") is not None else None
+            ion_mobility=float(im) if (im := peptide_id.getMetaValue("IM")) is not None else None,
             protein_list=[
                 accession.decode() for accession in peptide_hit.extractProteinAccessionsSet()
             ],