diff --git a/src/mol-data/db/column.ts b/src/mol-data/db/column.ts
index fa0e0920e905952132821dfca929964bc6869b75..d94afadcd76ea27c5425924cbd71e57d4cca0ec3 100644
--- a/src/mol-data/db/column.ts
+++ b/src/mol-data/db/column.ts
@@ -128,7 +128,7 @@ namespace Column {
     }
 
     export function mapToArray<T, S>(column: Column<T>, f: (v: T) => S, ctor?: ArrayCtor<S>): ArrayLike<S> {
-        return mapToArrayImpl(column, f, ctor || Array);
+        return mapToArrayImpl<T, S>(column, f, ctor || Array);
     }
 
     export function areEqual<T>(a: Column<T>, b: Column<T>) {