diff --git a/src/mol-state/object.ts b/src/mol-state/object.ts
index 3e2df3343df0b95b85698bbbbdabcfbda6dbbbd6..e8bdf73751d8d4b7fe63d5cffb7c6a834ba4204a 100644
--- a/src/mol-state/object.ts
+++ b/src/mol-state/object.ts
@@ -53,7 +53,7 @@ namespace StateObject {
     };
 }
 
-interface StateObjectCell {
+interface StateObjectCell<T = StateObject> {
     transform: Transform,
 
     // Which object was used as a parent to create data in this cell
@@ -68,7 +68,7 @@ interface StateObjectCell {
     } | undefined;
 
     errorText?: string,
-    obj?: StateObject
+    obj?: T
 }
 
 namespace StateObjectCell {
diff --git a/src/mol-state/state/selection.ts b/src/mol-state/state/selection.ts
index 5bb6010f5805c52ee41a79c8d31eac078229d648..828f7c9cf85a0926dae10d13bc6c675094939b64 100644
--- a/src/mol-state/state/selection.ts
+++ b/src/mol-state/state/selection.ts
@@ -29,7 +29,7 @@ namespace StateSelection {
     }
 
     function isObj(arg: any): arg is StateObjectCell {
-        return (arg as StateObjectCell).version !== void 0;
+        return (arg as StateObjectCell).version !== void 0 && (arg as StateObjectCell).transform !== void 0;
     }
 
     function isBuilder(arg: any): arg is Builder {
diff --git a/src/mol-state/transformer.ts b/src/mol-state/transformer.ts
index b10778f9f0741a0fbf4e80af14759489638f936a..3693eb5cae8aee0b7b20c2976c0dd9139727d7f5 100644
--- a/src/mol-state/transformer.ts
+++ b/src/mol-state/transformer.ts
@@ -5,7 +5,7 @@
  */
 
 import { Task } from 'mol-task';
-import { StateObject } from './object';
+import { StateObject, StateObjectCell } from './object';
 import { Transform } from './transform';
 import { ParamDefinition as PD } from 'mol-util/param-definition';
 import { StateAction } from './action';
@@ -24,6 +24,7 @@ export namespace Transformer {
     export type Params<T extends Transformer<any, any, any>> = T extends Transformer<any, any, infer P> ? P : unknown;
     export type From<T extends Transformer<any, any, any>> = T extends Transformer<infer A, any, any> ? A : unknown;
     export type To<T extends Transformer<any, any, any>> = T extends Transformer<any, infer B, any> ? B : unknown;
+    export type Cell<T extends Transformer<any, any, any>> = T extends Transformer<any, infer B, any> ? StateObjectCell<B> : unknown;
 
     export function is(obj: any): obj is Transformer {
         return !!obj && typeof (obj as Transformer).toAction === 'function' && typeof (obj as Transformer).apply === 'function';