diff --git a/src/legacy/server/capabilities/merge_capabilities.test.ts b/src/legacy/server/capabilities/merge_capabilities.test.ts
new file mode 100644
index 00000000000000..a73b81bdaf0a32
--- /dev/null
+++ b/src/legacy/server/capabilities/merge_capabilities.test.ts
@@ -0,0 +1,84 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { mergeCapabilities } from './merge_capabilities';
+
+const defaultProps = {
+  catalogue: {},
+  management: {},
+  navLinks: {},
+};
+
+test(`"{ foo: {} }" doesn't clobber "{ foo: { bar: true } }"`, () => {
+  const output1 = mergeCapabilities({ foo: { bar: true } }, { foo: {} });
+  expect(output1).toEqual({ ...defaultProps, foo: { bar: true } });
+
+  const output2 = mergeCapabilities({ foo: { bar: true } }, { foo: {} });
+  expect(output2).toEqual({ ...defaultProps, foo: { bar: true } });
+});
+
+test(`"{ foo: { bar: true } }" doesn't clobber "{ baz: { quz: true } }"`, () => {
+  const output1 = mergeCapabilities({ foo: { bar: true } }, { baz: { quz: true } });
+  expect(output1).toEqual({ ...defaultProps, foo: { bar: true }, baz: { quz: true } });
+
+  const output2 = mergeCapabilities({ baz: { quz: true } }, { foo: { bar: true } });
+  expect(output2).toEqual({ ...defaultProps, foo: { bar: true }, baz: { quz: true } });
+});
+
+test(`"{ foo: { bar: { baz: true } } }" doesn't clobber "{ foo: { bar: { quz: true } } }"`, () => {
+  const output1 = mergeCapabilities(
+    { foo: { bar: { baz: true } } },
+    { foo: { bar: { quz: true } } }
+  );
+  expect(output1).toEqual({ ...defaultProps, foo: { bar: { baz: true, quz: true } } });
+
+  const output2 = mergeCapabilities(
+    { foo: { bar: { quz: true } } },
+    { foo: { bar: { baz: true } } }
+  );
+  expect(output2).toEqual({ ...defaultProps, foo: { bar: { baz: true, quz: true } } });
+});
+
+test(`error is thrown if boolean and object clash`, () => {
+  expect(() => {
+    mergeCapabilities({ foo: { bar: { baz: true } } }, { foo: { bar: true } });
+  }).toThrowErrorMatchingInlineSnapshot(`"a boolean and an object can't be merged"`);
+
+  expect(() => {
+    mergeCapabilities({ foo: { bar: true } }, { foo: { bar: { baz: true } } });
+  }).toThrowErrorMatchingInlineSnapshot(`"a boolean and an object can't be merged"`);
+});
+
+test(`supports duplicates as long as the booleans are the same`, () => {
+  const output1 = mergeCapabilities({ foo: { bar: true } }, { foo: { bar: true } });
+  expect(output1).toEqual({ ...defaultProps, foo: { bar: true } });
+
+  const output2 = mergeCapabilities({ foo: { bar: false } }, { foo: { bar: false } });
+  expect(output2).toEqual({ ...defaultProps, foo: { bar: false } });
+});
+
+test(`error is thrown if merging "true" and "false"`, () => {
+  expect(() => {
+    mergeCapabilities({ foo: { bar: false } }, { foo: { bar: true } });
+  }).toThrowErrorMatchingInlineSnapshot(`"\\"true\\" and \\"false\\" can't be merged"`);
+
+  expect(() => {
+    mergeCapabilities({ foo: { bar: true } }, { foo: { bar: false } });
+  }).toThrowErrorMatchingInlineSnapshot(`"\\"true\\" and \\"false\\" can't be merged"`);
+});
diff --git a/src/legacy/server/capabilities/merge_capabilities.ts b/src/legacy/server/capabilities/merge_capabilities.ts
index b0b62f89748063..5fe31775ba32d8 100644
--- a/src/legacy/server/capabilities/merge_capabilities.ts
+++ b/src/legacy/server/capabilities/merge_capabilities.ts
@@ -17,6 +17,7 @@
  * under the License.
  */
 
+import typeDetect from 'type-detect';
 import { merge } from 'lodash';
 import { Capabilities } from '../../../core/public';
 
@@ -27,5 +28,17 @@ export const mergeCapabilities = (...sources: Array<Partial<Capabilities>>): Cap
       management: {},
       catalogue: {},
     },
-    ...sources
+    ...sources,
+    (a: any, b: any) => {
+      if (
+        (typeDetect(a) === 'boolean' && typeDetect(b) === 'Object') ||
+        (typeDetect(b) === 'boolean' && typeDetect(a) === 'Object')
+      ) {
+        throw new Error(`a boolean and an object can't be merged`);
+      }
+
+      if (typeDetect(a) === 'boolean' && typeDetect(b) === 'boolean' && a !== b) {
+        throw new Error(`"true" and "false" can't be merged`);
+      }
+    }
   );