diff --git a/src/IndexBy.ts b/src/IndexBy.ts
index 1bbea1b..99265f4 100644
--- a/src/IndexBy.ts
+++ b/src/IndexBy.ts
@@ -2,29 +2,21 @@ import { MaybeSelector } from "./MaybeSelector";
 import { Selector } from "./Selector";
 import { GetSignature } from "./Get";
 import { StringProperty } from "./util";
+import { Composable } from "./Composable";
+import { Dimensionality, Structure } from "./Discriminants";
 
-export type IndexBy<A, B, Params extends {} = {}> =
+export type IndexByOverloads<D extends Dimensionality, S extends Structure, A, B, Params extends {}> =
   B extends { [key: string]: infer C }
-  ? IndexByOverloads<A, B, C, Params>
-  : never
-
-export interface IndexByOverloads<A, B, C, Params> {
-  <K extends string>(key: K): MaybeSelector<A, C, Params & StringProperty<K>>
-  <K extends string>(key: K, defaultValue: C): Selector<A, C, Params & StringProperty<K>>
-  <K extends string>(key: K, getDefault: GetSignature<B, C, Params & StringProperty<K>>): Selector<A, C, Params & StringProperty<K>>
-}
-
-export type IndexByMaybe<A, B, Params extends {} = {}> =
-  B extends { [key: string]: infer C }
-  ? IndexByMaybeOverloads<A, B, C, Params>
+  ? {
+    <K extends string>(key: K)
+      : Composable.ComposeResult<A, C, Params & StringProperty<K>, D, Dimensionality.Maybe, S, Structure.Select>
+    <K extends string>(key: K, defaultValue: C)
+      : Composable.ComposeResult<A, C, Params & StringProperty<K>, D, Dimensionality.Single, S, Structure.Select>
+    <K extends string>(key: K, getDefault: GetSignature<B, C, Params & StringProperty<K>>)
+      : Composable.ComposeResult<A, C, Params & StringProperty<K>, D, Dimensionality.Single, S, Structure.Select>
+  }
   : never
 
-export interface IndexByMaybeOverloads<A, B, C, Params> {
-  <K extends string>(key: K): MaybeSelector<A, C, Params & StringProperty<K>>
-  <K extends string>(key: K, defaultValue: C): MaybeSelector<A, C, Params & StringProperty<K>>
-  <K extends string>(key: K, getDefault: GetSignature<B, C, Params & StringProperty<K>>): MaybeSelector<A, C, Params & StringProperty<K>>
-}
-
 export namespace IndexBy {
   const nullIfUndefined = <T>(x: T) => x === undefined ? null : x
 
diff --git a/src/MaybeSelector.spec.ts b/src/MaybeSelector.spec.ts
index 7b9a01c..e3d16a9 100644
--- a/src/MaybeSelector.spec.ts
+++ b/src/MaybeSelector.spec.ts
@@ -5,7 +5,6 @@ import { Get } from './Get';
 import { MaybeSelector } from './MaybeSelector';
 import { Converter } from './Converter';
 import { MaybeConverter } from './MaybeConverter';
-import { IndexBy } from './IndexBy';
 import { Biselect } from '.';
 import { MaybeGet } from './MaybeGet';
 
diff --git a/src/MaybeSelector.ts b/src/MaybeSelector.ts
index 5a0d43d..7d967d2 100644
--- a/src/MaybeSelector.ts
+++ b/src/MaybeSelector.ts
@@ -7,7 +7,7 @@ import { Selector } from './Selector'
 import { MaybeConverter } from './MaybeConverter'
 import { Converter } from './Converter'
 import { MaybeSelectorPropOverloads, Prop } from './Prop'
-import { IndexBy, IndexByMaybe } from './IndexBy'
+import { IndexBy, IndexByOverloads } from './IndexBy'
 import { Choose, ChooseOverloads } from './Choose';
 import { Extension } from './Extension';
 import { Memoize } from './Memoize';
@@ -36,7 +36,7 @@ export interface MaybeSelector<A, B, Params extends {} = {}> {
   modify: Modify<A, B, Params>
   compose: MaybeSelectorCompose<A, B, Params>
   prop: MaybeSelectorPropOverloads<A, B, Params>
-  indexBy: IndexByMaybe<A, B, Params>
+  indexBy: IndexByOverloads<Dimensionality.Maybe, Structure.Select, A, B, Params>
   choose: ChooseOverloads<Dimensionality.Maybe, Structure.Select, A, B, Params>
   ifDefined: IfDefinedOverloads<Dimensionality.Maybe, Structure.Select, A, B, Params>
   merge: Merge<A, B, Params>
diff --git a/src/Root.ts b/src/Root.ts
index 35955f4..0f4e865 100644
--- a/src/Root.ts
+++ b/src/Root.ts
@@ -1,13 +1,14 @@
-import { IndexBy } from "./IndexBy";
+import { IndexBy, IndexByOverloads } from "./IndexBy";
 import { SelectorPropOverloads, Prop } from "./Prop";
 import { MaybeConverter } from "./MaybeConverter";
 import { Choose } from "./Choose";
 import { Extension } from "./Extension";
 import { Memoize } from "./Memoize";
 import { Debug } from "./Debug";
+import { Dimensionality, Structure } from './Discriminants';
 
 export interface Root<A> {
-  indexBy: IndexBy<A, A>
+  indexBy: IndexByOverloads<Dimensionality.Single, Structure.Convert, A, A, {}>
   prop: SelectorPropOverloads<A, A>
   choose<B extends A>(typeGuard: (a: A) => a is B): MaybeConverter<A, B>
   extend: (newExt: Extension) => Root<A>
diff --git a/src/Selector.ts b/src/Selector.ts
index 61dcde7..0fd08de 100644
--- a/src/Selector.ts
+++ b/src/Selector.ts
@@ -6,7 +6,7 @@ import { MaybeConverter } from './MaybeConverter'
 import { Converter } from './Converter'
 import { Composable } from './Composable'
 import { SelectorPropOverloads, Prop } from './Prop'
-import { IndexBy } from './IndexBy';
+import { IndexBy, IndexByOverloads } from './IndexBy';
 import { Choose, ChooseOverloads } from './Choose';
 import { Extension } from './Extension';
 import { Memoize } from './Memoize';
@@ -35,7 +35,7 @@ export interface Selector<A, B, Params extends {} = {}> {
   modify: Modify<A, B, Params>
   compose: SelectorCompose<A, B, Params>
   prop: SelectorPropOverloads<A, B, Params>
-  indexBy: IndexBy<A, B, Params>
+  indexBy: IndexByOverloads<Dimensionality.Single, Structure.Select, A, B, Params>
   choose: ChooseOverloads<Dimensionality.Single, Structure.Select, A, B, Params>
   ifDefined: IfDefinedOverloads<Dimensionality.Single, Structure.Select, A, B, Params>
   merge: Merge<A, B, Params>