diff --git a/src/babel/transformation/transformers/es6/classes.js b/src/babel/transformation/transformers/es6/classes.js
index 4af1e12c32..649adcf86d 100644
--- a/src/babel/transformation/transformers/es6/classes.js
+++ b/src/babel/transformation/transformers/es6/classes.js
@@ -552,6 +552,11 @@ class ClassTransformer {
         this.instancePropBody.push(t.expressionStatement(
           t.assignmentExpression("=", t.memberExpression(t.thisExpression(), node.key), node.value)
         ));
+
+        node.value = null;
+      }
+
+      if (!node.value) {
         node.value = t.identifier("undefined");
       }
 
diff --git a/test/core/fixtures/transformation/es7.class-properties/instance-undefined/actual.js b/test/core/fixtures/transformation/es7.class-properties/instance-undefined/actual.js
new file mode 100644
index 0000000000..a36cdd975c
--- /dev/null
+++ b/test/core/fixtures/transformation/es7.class-properties/instance-undefined/actual.js
@@ -0,0 +1,3 @@
+class Foo {
+  bar;
+}
diff --git a/test/core/fixtures/transformation/es7.class-properties/instance-undefined/expected.js b/test/core/fixtures/transformation/es7.class-properties/instance-undefined/expected.js
new file mode 100644
index 0000000000..4fed431790
--- /dev/null
+++ b/test/core/fixtures/transformation/es7.class-properties/instance-undefined/expected.js
@@ -0,0 +1,14 @@
+"use strict";
+
+var Foo = (function () {
+  function Foo() {
+    babelHelpers.classCallCheck(this, Foo);
+  }
+
+  babelHelpers.createClass(Foo, [{
+    key: "bar",
+    value: undefined,
+    enumerable: true
+  }]);
+  return Foo;
+})();
\ No newline at end of file
diff --git a/test/core/fixtures/transformation/es7.class-properties/static-undefined/actual.js b/test/core/fixtures/transformation/es7.class-properties/static-undefined/actual.js
new file mode 100644
index 0000000000..4ee31b9c35
--- /dev/null
+++ b/test/core/fixtures/transformation/es7.class-properties/static-undefined/actual.js
@@ -0,0 +1,3 @@
+class Foo {
+  static bar;
+}
diff --git a/test/core/fixtures/transformation/es7.class-properties/static-undefined/exec.js b/test/core/fixtures/transformation/es7.class-properties/static-undefined/exec.js
new file mode 100644
index 0000000000..0771105a61
--- /dev/null
+++ b/test/core/fixtures/transformation/es7.class-properties/static-undefined/exec.js
@@ -0,0 +1,6 @@
+class Foo {
+  static num;
+}
+
+assert.equal("num" in Foo, true);
+assert.equal(Foo.num, undefined);
diff --git a/test/core/fixtures/transformation/es7.class-properties/static-undefined/expected.js b/test/core/fixtures/transformation/es7.class-properties/static-undefined/expected.js
new file mode 100644
index 0000000000..f5c17bfa15
--- /dev/null
+++ b/test/core/fixtures/transformation/es7.class-properties/static-undefined/expected.js
@@ -0,0 +1,14 @@
+"use strict";
+
+var Foo = (function () {
+  function Foo() {
+    babelHelpers.classCallCheck(this, Foo);
+  }
+
+  babelHelpers.createClass(Foo, null, [{
+    key: "bar",
+    value: undefined,
+    enumerable: true
+  }]);
+  return Foo;
+})();