diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9c440252bfc5..1f66686e4a4e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,7 @@
 - `[jest-snapshot]` Properly indent new snapshots in the presences of existing ones ([#9523](https://github.com/facebook/jest/pull/9523))
 - `[jest-transform]` Correct sourcemap behavior for transformed and instrumented code ([#9460](https://github.com/facebook/jest/pull/9460))
 - `[jest-transform]` Allow instrumentation of transformed files with weird file extensions ([#9589](https://github.com/facebook/jest/pull/9589))
+- `[@jest/types]` Make `ConfigGlobals` an interface to allow for declaration merging. ([#9570](https://github.com/facebook/jest/pull/9570))
 - `[pretty-format]` Export `OldPlugin` type ([#9491](https://github.com/facebook/jest/pull/9491))
 
 ### Chore & Maintenance
diff --git a/packages/jest-config/package.json b/packages/jest-config/package.json
index 6f3da60d5a31..2ecba2db62c6 100644
--- a/packages/jest-config/package.json
+++ b/packages/jest-config/package.json
@@ -15,6 +15,7 @@
     "@jest/types": "^25.1.0",
     "babel-jest": "^25.1.0",
     "chalk": "^3.0.0",
+    "deepmerge": "^4.2.2",
     "glob": "^7.1.1",
     "jest-environment-jsdom": "^25.1.0",
     "jest-environment-node": "^25.1.0",
diff --git a/packages/jest-config/src/__tests__/normalize.test.js b/packages/jest-config/src/__tests__/normalize.test.js
index 1d6f786ee06e..ee4a6658f112 100644
--- a/packages/jest-config/src/__tests__/normalize.test.js
+++ b/packages/jest-config/src/__tests__/normalize.test.js
@@ -1251,9 +1251,11 @@ describe('preset with globals', () => {
       '/node_modules/global-foo/jest-preset.json',
       () => ({
         globals: {
+          __DEV__: false,
           config: {
             hereToStay: 'This should stay here',
           },
+          myString: 'hello world',
         },
       }),
       {virtual: true},
@@ -1268,9 +1270,11 @@ describe('preset with globals', () => {
     const {options} = normalize(
       {
         globals: {
+          __DEV__: true,
           config: {
             sideBySide: 'This should also live another day',
           },
+          myString: 'hello sunshine',
           textValue: 'This is just text',
         },
         preset: 'global-foo',
@@ -1279,17 +1283,15 @@ describe('preset with globals', () => {
       {},
     );
 
-    expect(options).toEqual(
-      expect.objectContaining({
-        globals: {
-          config: {
-            hereToStay: 'This should stay here',
-            sideBySide: 'This should also live another day',
-          },
-          textValue: 'This is just text',
-        },
-      }),
-    );
+    expect(options.globals).toEqual({
+      __DEV__: true,
+      config: {
+        hereToStay: 'This should stay here',
+        sideBySide: 'This should also live another day',
+      },
+      myString: 'hello sunshine',
+      textValue: 'This is just text',
+    });
   });
 });
 
diff --git a/packages/jest-config/src/normalize.ts b/packages/jest-config/src/normalize.ts
index dafd3f0232e2..e20d7026b108 100644
--- a/packages/jest-config/src/normalize.ts
+++ b/packages/jest-config/src/normalize.ts
@@ -17,6 +17,7 @@ import micromatch = require('micromatch');
 import {sync as realpath} from 'realpath-native';
 import Resolver = require('jest-resolve');
 import {replacePathSepForRegex} from 'jest-regex-util';
+import merge = require('deepmerge');
 import validatePattern from './validatePattern';
 import getMaxWorkers from './getMaxWorkers';
 import {
@@ -112,12 +113,7 @@ const mergeGlobalsWithPreset = (
   preset: Config.InitialOptions,
 ) => {
   if (options['globals'] && preset['globals']) {
-    for (const p in preset['globals']) {
-      options['globals'][p] = {
-        ...preset['globals'][p],
-        ...options['globals'][p],
-      };
-    }
+    options['globals'] = merge(preset['globals'], options['globals']);
   }
 };
 
diff --git a/packages/jest-types/src/Config.ts b/packages/jest-types/src/Config.ts
index 5bb9eea84b11..dd55118c427d 100644
--- a/packages/jest-types/src/Config.ts
+++ b/packages/jest-types/src/Config.ts
@@ -27,7 +27,9 @@ export type HasteConfig = {
 export type ReporterConfig = [string, Record<string, unknown>];
 export type TransformerConfig = [string, Record<string, unknown>];
 
-export type ConfigGlobals = Record<string, any>;
+export interface ConfigGlobals {
+  [K: string]: unknown;
+}
 
 export type DefaultOptions = {
   automock: boolean;
diff --git a/yarn.lock b/yarn.lock
index ea1bce583f4c..98ed8db9afe2 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -5221,6 +5221,11 @@ deepmerge@^3.2.0:
   resolved "https://registry.yarnpkg.com/deepmerge/-/deepmerge-3.3.0.tgz#d3c47fd6f3a93d517b14426b0628a17b0125f5f7"
   integrity sha512-GRQOafGHwMHpjPx9iCvTgpu9NojZ49q794EEL94JVEw6VaeA8XTUyBKvAkOOjBX9oJNiV6G3P+T+tihFjo2TqA==
 
+deepmerge@^4.2.2:
+  version "4.2.2"
+  resolved "https://registry.yarnpkg.com/deepmerge/-/deepmerge-4.2.2.tgz#44d2ea3679b8f4d4ffba33f03d865fc1e7bf4955"
+  integrity sha512-FJ3UgI4gIl+PHZm53knsuSFpE+nESMr7M4v9QcgB7S63Kj/6WqMiFQJpBBYz1Pt+66bZpP3Q7Lye0Oo9MPKEdg==
+
 defaults@^1.0.3:
   version "1.0.3"
   resolved "https://registry.yarnpkg.com/defaults/-/defaults-1.0.3.tgz#c656051e9817d9ff08ed881477f3fe4019f3ef7d"