diff --git a/src/mol-model/structure/model/properties/hierarchy.ts b/src/mol-model/structure/model/properties/hierarchy.ts
index 92d5f006a82c551c31a1904e4d7317363f585f8e..773e091d845fb23e1dda9c2c887df824d2b55c70 100644
--- a/src/mol-model/structure/model/properties/hierarchy.ts
+++ b/src/mol-model/structure/model/properties/hierarchy.ts
@@ -59,7 +59,7 @@ export interface Segments {
 export interface Keys {
     // indicate whether the keys form an increasing sequence and within each chain, sequence numbers
     // are in increasing order.
-    // monotonous sequences enable for example faster secodnary structure assignment.
+    // monotonous sequences enable for example faster secondary structure assignment.
     isMonotonous: boolean,
 
     // assign a key to each residue index.