diff --git a/src/index.js b/src/index.js
index 6f493cf..5ae7b7b 100644
--- a/src/index.js
+++ b/src/index.js
@@ -27,7 +27,10 @@ exports.Store = class Store {
             for (let module of modules) {
               if (state[module]) state = state[module]
               else {
-                throw new Error(`[vuex-mock-store] module ${key} not defined in state:`, this.state)
+                throw new Error(
+                  `[vuex-mock-store] module "${key.slice(0, -1)}" not defined in state:`,
+                  this.state
+                )
               }
             }
 
diff --git a/test/index.spec.js b/test/index.spec.js
index 0150616..f6188ef 100644
--- a/test/index.spec.js
+++ b/test/index.spec.js
@@ -1,6 +1,7 @@
 const { Store } = require('../src')
 const Helper = require('./Helper')
 const { mount } = require('@vue/test-utils')
+const { mapState } = require('vuex')
 
 describe('Store Mock', () => {
   it('copies the state', () => {
@@ -72,5 +73,20 @@ describe('Store Mock', () => {
 
       expect(wrapper.vm.getter).toBe(1)
     })
+
+    it('throws with non-defined state', () => {
+      /** @type {import('@vue/test-utils').Wrapper<Helper>} */
+      let wrapper = mount(
+        {
+          render: () => null,
+          computed: mapState('nonExistent', ['a']),
+        },
+        { mocks }
+      )
+      expect(() => {
+        // eslint-disable-next-line no-unused-expressions
+        wrapper.vm.a
+      }).toThrow(/module "nonExistent" not defined in state/)
+    })
   })
 })