diff --git a/packages/gatsby/src/redux/reducers/index.js b/packages/gatsby/src/redux/reducers/index.js
index 612df7a25eebb..426b53f021d22 100644
--- a/packages/gatsby/src/redux/reducers/index.js
+++ b/packages/gatsby/src/redux/reducers/index.js
@@ -1,6 +1,7 @@
 const reduxNodes = require(`./nodes`)
 const lokiNodes = require(`../../db/loki/nodes`).reducer
 import { redirectsReducer } from "./redirects"
+import { schemaReducer } from "./schema"
 import { staticQueryComponentsReducer } from "./static-query-components"
 import { statusReducer } from "./status"
 import { webpackCompilationHashReducer } from "./webpack-compilation-hash"
@@ -55,7 +56,7 @@ module.exports = {
   flattenedPlugins: require(`./flattened-plugins`),
   config: require(`./config`),
   pages: require(`./pages`),
-  schema: require(`./schema`),
+  schema: schemaReducer,
   status: statusReducer,
   componentDataDependencies: require(`./component-data-dependencies`),
   components: require(`./components`),
diff --git a/packages/gatsby/src/redux/reducers/schema.js b/packages/gatsby/src/redux/reducers/schema.js
deleted file mode 100644
index 01fbacb86082e..0000000000000
--- a/packages/gatsby/src/redux/reducers/schema.js
+++ /dev/null
@@ -1,8 +0,0 @@
-module.exports = (state = {}, action) => {
-  switch (action.type) {
-    case `SET_SCHEMA`:
-      return action.payload
-    default:
-      return state
-  }
-}
diff --git a/packages/gatsby/src/redux/reducers/schema.ts b/packages/gatsby/src/redux/reducers/schema.ts
new file mode 100644
index 0000000000000..1078072b56969
--- /dev/null
+++ b/packages/gatsby/src/redux/reducers/schema.ts
@@ -0,0 +1,13 @@
+import { ActionsUnion, IGatsbyState } from "../types"
+
+export const schemaReducer = (
+  state: IGatsbyState["schema"] | {} = {},
+  action: ActionsUnion
+): IGatsbyState["schema"] | {} => {
+  switch (action.type) {
+    case `SET_SCHEMA`:
+      return action.payload
+    default:
+      return state
+  }
+}
diff --git a/packages/gatsby/src/redux/types.ts b/packages/gatsby/src/redux/types.ts
index d6cce1796d385..0599580d1eec6 100644
--- a/packages/gatsby/src/redux/types.ts
+++ b/packages/gatsby/src/redux/types.ts
@@ -225,6 +225,7 @@ export type ActionsUnion =
   | IReplaceStaticQueryAction
   | ISetPluginStatusAction
   | ISetProgramStatusAction
+  | ISetSchemaAction
   | ISetWebpackCompilationHashAction
   | IUpdatePluginsHashAction
 
@@ -399,3 +400,8 @@ export interface ISetPluginStatusAction {
     [key: string]: any
   }
 }
+
+export interface ISetSchemaAction {
+  type: `SET_SCHEMA`
+  payload: IGatsbyState["schema"]
+}