diff --git a/lib/rules/no-side-effects-in-computed-properties.js b/lib/rules/no-side-effects-in-computed-properties.js
index 9ac247d17..83035ec50 100644
--- a/lib/rules/no-side-effects-in-computed-properties.js
+++ b/lib/rules/no-side-effects-in-computed-properties.js
@@ -12,8 +12,9 @@ function create (context) {
   return Object.assign({},
     {
       // this.xxx <=|+=|-=>
-      'AssignmentExpression > MemberExpression' (node) {
-        if (utils.parseMemberExpression(node)[0] === 'this') {
+      'AssignmentExpression' (node) {
+        if (node.left.type !== 'MemberExpression') return
+        if (utils.parseMemberExpression(node.left)[0] === 'this') {
           forbiddenNodes.push(node)
         }
       },
diff --git a/tests/lib/rules/no-side-effects-in-computed-properties.js b/tests/lib/rules/no-side-effects-in-computed-properties.js
index a84e6fae8..9e63b3079 100644
--- a/tests/lib/rules/no-side-effects-in-computed-properties.js
+++ b/tests/lib/rules/no-side-effects-in-computed-properties.js
@@ -105,6 +105,18 @@ ruleTester.run('no-side-effects-in-computed-properties', rule, {
         }
       })`,
       parserOptions
+    },
+    {
+      code: `Vue.component('test', {
+        computed: {
+          test () {
+            let a;
+            a = this.something
+            return a
+          },
+        }
+      })`,
+      parserOptions
     }
   ],
   invalid: [
@@ -128,6 +140,10 @@ ruleTester.run('no-side-effects-in-computed-properties', rule, {
             const test = this.another.something.push('example')
             return 'something'
           },
+          test5() {
+            this.something[index] = thing[index]
+            return this.something
+          },
         }
       })`,
       parserOptions,
@@ -146,6 +162,9 @@ ruleTester.run('no-side-effects-in-computed-properties', rule, {
       }, {
         line: 17,
         message: 'Unexpected side effect in "test4" computed property.'
+      }, {
+        line: 21,
+        message: 'Unexpected side effect in "test5" computed property.'
       }]
     },
     {