diff --git a/packages/babel-helper-function-name/src/index.js b/packages/babel-helper-function-name/src/index.js
index bdce1f819c12..b736d76f575a 100644
--- a/packages/babel-helper-function-name/src/index.js
+++ b/packages/babel-helper-function-name/src/index.js
@@ -179,7 +179,7 @@ export default function({ node, parent, scope, id }, localBinding = false) {
         return;
       }
     }
-  } else if (t.isAssignmentExpression(parent)) {
+  } else if (t.isAssignmentExpression(parent, { operator: "=" })) {
     // foo = function () {};
     id = parent.left;
   } else if (!id) {
diff --git a/packages/babel-plugin-transform-function-name/test/fixtures/function-name/function-assignment/input.js b/packages/babel-plugin-transform-function-name/test/fixtures/function-name/function-assignment/input.js
index e8efb0c87a4e..3725d0fe7260 100644
--- a/packages/babel-plugin-transform-function-name/test/fixtures/function-name/function-assignment/input.js
+++ b/packages/babel-plugin-transform-function-name/test/fixtures/function-name/function-assignment/input.js
@@ -11,3 +11,5 @@ baz = 12;
 bar = function() {
   bar();
 };
+
+qux += function() {}
diff --git a/packages/babel-plugin-transform-function-name/test/fixtures/function-name/function-assignment/output.js b/packages/babel-plugin-transform-function-name/test/fixtures/function-name/function-assignment/output.js
index d0313b653d93..8527bf833e5b 100644
--- a/packages/babel-plugin-transform-function-name/test/fixtures/function-name/function-assignment/output.js
+++ b/packages/babel-plugin-transform-function-name/test/fixtures/function-name/function-assignment/output.js
@@ -23,3 +23,5 @@ bar = function (_bar) {
 }(function () {
   bar();
 });
+
+qux += function () {};