diff --git a/client/src/reducers/continuousSelection.ts b/client/src/reducers/continuousSelection.ts
index d80cffe6..7e31b5c8 100644
--- a/client/src/reducers/continuousSelection.ts
+++ b/client/src/reducers/continuousSelection.ts
@@ -1,7 +1,24 @@
-import { makeContinuousDimensionName } from "../util/nameCreators";
+import { Action } from "redux";
+import type { RootState } from ".";
+import {
+  ContinuousNamespace,
+  makeContinuousDimensionName,
+} from "../util/nameCreators";
 
-// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types, @typescript-eslint/no-explicit-any -- - FIXME: disabled temporarily on migrate to TS.
-const ContinuousSelection = (state = {}, action: any) => {
+export interface ContinuousSelectionAction extends Action<string> {
+  continuousNamespace: ContinuousNamespace;
+  selection: string;
+  range: [number, number];
+}
+
+export interface ContinuousSelectionState {
+  [name: string]: [number, number];
+}
+
+const ContinuousSelection = (
+  state: ContinuousSelectionState = {},
+  action: ContinuousSelectionAction
+): RootState => {
   switch (action.type) {
     case "reset subset":
     case "subset to selection":
@@ -25,7 +42,6 @@ const ContinuousSelection = (state = {}, action: any) => {
         action.continuousNamespace,
         action.selection
       );
-      // @ts-expect-error ts-migrate(2537) FIXME: Type '{}' has no matching index signature for type... Remove this comment to see the full error message
       const { [name]: deletedField, ...newState } = state;
       return newState;
     }