diff --git a/lib/6to5/transformation/modules/_default.js b/lib/6to5/transformation/modules/_default.js
index 495ffd60c5..300c12ab18 100644
--- a/lib/6to5/transformation/modules/_default.js
+++ b/lib/6to5/transformation/modules/_default.js
@@ -212,6 +212,12 @@ DefaultFormatter.prototype.getExternalReference = function (node, nodes) {
   }
 };
 
+DefaultFormatter.prototype.checkExportIdentifier = function (node) {
+  if (t.isIdentifier(node, { name: "__esModule" })) {
+    throw this.file.errorWithNode(node, "Illegal export __esModule - this is used internally for CommonJS interop");
+  }
+};
+
 DefaultFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
   var inherits = false;
   if (node.specifiers.length === 1) inherits = node;
@@ -251,6 +257,7 @@ DefaultFormatter.prototype.buildExportsWildcard = function (objectIdentifier) {
 };
 
 DefaultFormatter.prototype.buildExportsAssignment = function (id, init) {
+  this.checkExportIdentifier(id);
   return util.template("exports-assign", {
     VALUE: init,
     KEY:   id
diff --git a/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule-2/actual.js b/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule-2/actual.js
new file mode 100644
index 0000000000..2d4f3f2cd7
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule-2/actual.js
@@ -0,0 +1 @@
+export { __esModule };
diff --git a/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule-2/options.json b/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule-2/options.json
new file mode 100644
index 0000000000..5e33c8dbe1
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule-2/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "Illegal export __esModule - this is used internally for CommonJS interop"
+}
diff --git a/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule/actual.js b/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule/actual.js
new file mode 100644
index 0000000000..c8e52fd594
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule/actual.js
@@ -0,0 +1 @@
+export var __esModule = false;
diff --git a/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule/options.json b/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule/options.json
new file mode 100644
index 0000000000..5e33c8dbe1
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-common/illegal-export-esmodule/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "Illegal export __esModule - this is used internally for CommonJS interop"
+}