diff --git a/src/mol-model-formats/structure/mmcif/parser.ts b/src/mol-model-formats/structure/mmcif/parser.ts
index 4c4067686817246967561fe134080f0d91809a5b..4c92a0b9e5c6979b26c9b051be1218bf95406c44 100644
--- a/src/mol-model-formats/structure/mmcif/parser.ts
+++ b/src/mol-model-formats/structure/mmcif/parser.ts
@@ -324,14 +324,13 @@ function splitTable<T extends Table<any>>(table: T, col: Column<number>) {
 }
 
 async function readIHM(ctx: RuntimeContext, format: mmCIF_Format, formatData: FormatData) {
-    if (format.data.atom_site._rowCount && !format.data.atom_site.ihm_model_id.isDefined) {
-        throw new Error('expected _atom_site.ihm_model_id to be defined')
-    }
+    // when `atom_site.ihm_model_id` is undefined fall back to `atom_site.pdbx_PDB_model_num`
+    const atom_sites_modelColumn = format.data.atom_site.ihm_model_id.isDefined ? format.data.atom_site.ihm_model_id : format.data.atom_site.pdbx_PDB_model_num
 
     const { ihm_model_list } = format.data;
     const entities = getEntities(format)
 
-    const atom_sites = splitTable(format.data.atom_site, format.data.atom_site.ihm_model_id);
+    const atom_sites = splitTable(format.data.atom_site, atom_sites_modelColumn);
     // TODO: will coarse IHM records require sorting or will we trust it?
     // ==> Probably implement a sort as as well and store the sourceIndex same as with atomSite
     // If the sorting is implemented, updated mol-model/structure/properties: atom.sourceIndex
diff --git a/src/mol-plugin/state/transforms/helpers.ts b/src/mol-plugin/state/transforms/helpers.ts
index 730f140e5e979cf3c4aff7c65504379c46ec73f9..2a72f7a52fdb7e631e41519fa8fca721dc389c09 100644
--- a/src/mol-plugin/state/transforms/helpers.ts
+++ b/src/mol-plugin/state/transforms/helpers.ts
@@ -42,7 +42,7 @@ export function getStructureTransparency(structure: Structure, script: Script, v
  * Attaches ComputedSecondaryStructure property when unavailable in sourceData
  */
 export async function ensureSecondaryStructure(s: Structure) {
-    if (s.model.sourceData.kind === 'mmCIF') {
+    if (s.model && s.model.sourceData.kind === 'mmCIF') {
         if (!s.model.sourceData.data.struct_conf.id.isDefined && !s.model.sourceData.data.struct_sheet_range.id.isDefined) {
             await ComputedSecondaryStructure.attachFromCifOrCompute(s)
         }