diff --git a/src/prefixmaps/data/linked_data.csv b/src/prefixmaps/data/linked_data.csv
index 041d713..f776233 100644
--- a/src/prefixmaps/data/linked_data.csv
+++ b/src/prefixmaps/data/linked_data.csv
@@ -4,6 +4,7 @@ linkml,biolink,https://w3id.org/biolink/vocab/,canonical
 linkml,dcmitype,http://purl.org/dc/dcmitype/,canonical
 linkml,dcterms,http://purl.org/dc/terms/,canonical
 linkml,foaf,http://xmlns.com/foaf/0.1/,canonical
+linkml,ICD10CM,https://www.icd10data.com/search?s=,canonical
 linkml,linkml,https://w3id.org/linkml/,canonical
 linkml,NANDO,http://identifiers.org/NANDO:,canonical
 linkml,NCIThesaurus,http://ncicb.nci.nih.gov/xml/owl/EVS/Thesaurus.owl#,canonical
diff --git a/src/prefixmaps/data/linked_data.curated.yaml b/src/prefixmaps/data/linked_data.curated.yaml
index e04cb68..593b77d 100644
--- a/src/prefixmaps/data/linked_data.curated.yaml
+++ b/src/prefixmaps/data/linked_data.curated.yaml
@@ -33,3 +33,6 @@ prefixes:
   dcmitype: http://purl.org/dc/dcmitype/
   wgs: http://www.w3.org/2003/01/geo/wgs84_pos#
   xml: http://www.w3.org/XML/1998/namespace
+  # Bioregistry's URI format for ICD-10-CM. Its icd.codes provider, which older bioregistry
+  # releases made canonical, has been dead since 2025-07 and is marked "gone" upstream.
+  ICD10CM: https://www.icd10data.com/search?s=
diff --git a/src/prefixmaps/data/merged.csv b/src/prefixmaps/data/merged.csv
index 6c3de9d..e25630c 100644
--- a/src/prefixmaps/data/merged.csv
+++ b/src/prefixmaps/data/merged.csv
@@ -6932,7 +6932,8 @@ merged,ICD10,https://icdcodelookup.com/icd-10/codes/,prefix_alias,bioregistry
 merged,ICD10,https://identifiers.org/icd/,prefix_alias,bioregistry
 merged,ICD10,https://identifiers.org/icd:,prefix_alias,bioregistry
 merged,ICD10,https://n2t.net/icd:,prefix_alias,bioregistry
-merged,ICD10CM,https://icd.codes/icd10cm/,canonical,bioregistry
+merged,ICD10CM,https://www.icd10data.com/search?s=,canonical,linkml
+merged,ICD10CM,https://icd.codes/icd10cm/,prefix_alias,bioregistry
 merged,ICD10CM,http://bioregistry.io/ICD10CM:,prefix_alias,bioregistry
 merged,ICD10CM,http://icd.codes/icd10cm/,prefix_alias,bioregistry
 merged,ICD10CM,http://purl.bioontology.org/ontology/ICD10CM/,prefix_alias,bioregistry
diff --git a/src/prefixmaps/data/merged.monarch.csv b/src/prefixmaps/data/merged.monarch.csv
index b87346c..7684b8d 100644
--- a/src/prefixmaps/data/merged.monarch.csv
+++ b/src/prefixmaps/data/merged.monarch.csv
@@ -6932,7 +6932,8 @@ merged.monarch,ICD10,https://icdcodelookup.com/icd-10/codes/,prefix_alias,bioreg
 merged.monarch,ICD10,https://identifiers.org/icd/,prefix_alias,bioregistry
 merged.monarch,ICD10,https://identifiers.org/icd:,prefix_alias,bioregistry
 merged.monarch,ICD10,https://n2t.net/icd:,prefix_alias,bioregistry
-merged.monarch,ICD10CM,https://icd.codes/icd10cm/,canonical,bioregistry
+merged.monarch,ICD10CM,https://www.icd10data.com/search?s=,canonical,linkml
+merged.monarch,ICD10CM,https://icd.codes/icd10cm/,prefix_alias,bioregistry
 merged.monarch,ICD10CM,http://bioregistry.io/ICD10CM:,prefix_alias,bioregistry
 merged.monarch,ICD10CM,http://icd.codes/icd10cm/,prefix_alias,bioregistry
 merged.monarch,ICD10CM,http://purl.bioontology.org/ontology/ICD10CM/,prefix_alias,bioregistry
diff --git a/src/prefixmaps/data/merged.oak.csv b/src/prefixmaps/data/merged.oak.csv
index 6a45ae8..8cd35d7 100644
--- a/src/prefixmaps/data/merged.oak.csv
+++ b/src/prefixmaps/data/merged.oak.csv
@@ -6932,7 +6932,8 @@ merged.oak,ICD10,https://icdcodelookup.com/icd-10/codes/,prefix_alias,bioregistr
 merged.oak,ICD10,https://identifiers.org/icd/,prefix_alias,bioregistry
 merged.oak,ICD10,https://identifiers.org/icd:,prefix_alias,bioregistry
 merged.oak,ICD10,https://n2t.net/icd:,prefix_alias,bioregistry
-merged.oak,ICD10CM,https://icd.codes/icd10cm/,canonical,bioregistry
+merged.oak,ICD10CM,https://www.icd10data.com/search?s=,canonical,linkml
+merged.oak,ICD10CM,https://icd.codes/icd10cm/,prefix_alias,bioregistry
 merged.oak,ICD10CM,http://bioregistry.io/ICD10CM:,prefix_alias,bioregistry
 merged.oak,ICD10CM,http://icd.codes/icd10cm/,prefix_alias,bioregistry
 merged.oak,ICD10CM,http://purl.bioontology.org/ontology/ICD10CM/,prefix_alias,bioregistry
diff --git a/tests/test_core/test_prefixmaps.py b/tests/test_core/test_prefixmaps.py
index 565a2c9..f19709e 100644
--- a/tests/test_core/test_prefixmaps.py
+++ b/tests/test_core/test_prefixmaps.py
@@ -229,3 +229,23 @@ def test_synonyms(self):
         for curie in others:
             with self.subTest(curie=curie):
                 self.assertEqual(canonical, converter.standardize_curie(curie))
+
+    def test_curated_icd10cm_prefix(self):
+        """ICD10CM is curated in linked_data to follow Bioregistry's URI format.
+
+        Older bioregistry releases made the dead icd.codes namespace canonical, see #80.
+        """
+        canonical = "https://www.icd10data.com/search?s="
+        for name in ["linked_data", "merged", "merged.monarch", "merged.oak"]:
+            with self.subTest(context=name):
+                ctxt = load_context(name)
+                self.assertEqual(canonical, ctxt.as_dict()["ICD10CM"])
+                self.assertEqual("ICD10CM", ctxt.as_inverted_dict()[canonical])
+        # the dead icd.codes namespace and the BioPortal PURL stay as aliases
+        aliases = {
+            pe.namespace
+            for pe in self.dyn_merged_context.prefix_expansions
+            if pe.prefix == "ICD10CM" and pe.status == StatusType.prefix_alias
+        }
+        self.assertIn("https://icd.codes/icd10cm/", aliases)
+        self.assertIn("http://purl.bioontology.org/ontology/ICD10CM/", aliases)