diff --git a/packages/babel-cli/test/fixtures/babel-external-helpers/--whitelist/stdout.txt b/packages/babel-cli/test/fixtures/babel-external-helpers/--whitelist/stdout.txt
index 8b78039c1add..d75b52e29f44 100644
--- a/packages/babel-cli/test/fixtures/babel-external-helpers/--whitelist/stdout.txt
+++ b/packages/babel-cli/test/fixtures/babel-external-helpers/--whitelist/stdout.txt
@@ -14,6 +14,9 @@
   function _createClass(Constructor, protoProps, staticProps) {
     if (protoProps) _defineProperties(Constructor.prototype, protoProps);
     if (staticProps) _defineProperties(Constructor, staticProps);
+    Object.defineProperty(Constructor, "prototype", {
+      writable: false
+    });
     return Constructor;
   }
 
diff --git a/packages/babel-helpers/src/helpers.ts b/packages/babel-helpers/src/helpers.ts
index b288be59b933..891aad0d2815 100644
--- a/packages/babel-helpers/src/helpers.ts
+++ b/packages/babel-helpers/src/helpers.ts
@@ -223,6 +223,7 @@ helpers.createClass = helper("7.0.0-beta.0")`
   export default function _createClass(Constructor, protoProps, staticProps) {
     if (protoProps) _defineProperties(Constructor.prototype, protoProps);
     if (staticProps) _defineProperties(Constructor, staticProps);
+    Object.defineProperty(Constructor, "prototype", { writable: false });
     return Constructor;
   }
 `;
@@ -334,12 +335,15 @@ helpers.inherits = helper("7.0.0-beta.0")`
     if (typeof superClass !== "function" && superClass !== null) {
       throw new TypeError("Super expression must either be null or a function");
     }
-    subClass.prototype = Object.create(superClass && superClass.prototype, {
-      constructor: {
-        value: subClass,
-        writable: true,
-        configurable: true
-      }
+    Object.defineProperty(subClass, "prototype", {
+      value: Object.create(superClass && superClass.prototype, {
+        constructor: {
+          value: subClass,
+          writable: true,
+          configurable: true
+        }
+      }),
+      writable: false,
     });
     if (superClass) setPrototypeOf(subClass, superClass);
   }
diff --git a/packages/babel-plugin-transform-classes/src/transformClass.ts b/packages/babel-plugin-transform-classes/src/transformClass.ts
index c25732f717a7..e1240d274c57 100644
--- a/packages/babel-plugin-transform-classes/src/transformClass.ts
+++ b/packages/babel-plugin-transform-classes/src/transformClass.ts
@@ -60,6 +60,7 @@ export default function transformClass(
     pushedInherits: false,
     protoAlias: null,
     isLoose: false,
+    createClassInjected: false,
 
     dynamicKeys: new Map(),
 
@@ -93,6 +94,10 @@ export default function transformClass(
     },
   ]);
 
+  function createClassHelper(args) {
+    return t.callExpression(classState.file.addHelper("createClass"), args);
+  }
+
   /**
    * Creates a class constructor or bail out if there is none
    */
@@ -240,11 +245,8 @@ export default function transformClass(
       }
       args = args.slice(0, lastNonNullIndex + 1);
 
-      body.push(
-        t.expressionStatement(
-          t.callExpression(classState.file.addHelper("createClass"), args),
-        ),
-      );
+      body.push(t.expressionStatement(createClassHelper(args)));
+      classState.createClassInjected = true;
     }
   }
 
@@ -737,10 +739,15 @@ export default function transformClass(
 
     if (constructorOnly) {
       // named class with only a constructor
-      return t.toExpression(body[0]);
+      return createClassHelper([t.toExpression(body[0])]);
+    }
+
+    let returnArg = t.cloneNode(classState.classRef);
+    if (!classState.createClassInjected) {
+      returnArg = createClassHelper([returnArg]);
     }
 
-    body.push(t.returnStatement(t.cloneNode(classState.classRef)));
+    body.push(t.returnStatement(returnArg));
     const container = t.arrowFunctionExpression(
       closureParams,
       t.blockStatement(body, directives),
diff --git a/packages/babel-plugin-transform-classes/test/fixtures/exec/prototype-descriptor.js b/packages/babel-plugin-transform-classes/test/fixtures/exec/prototype-descriptor.js
new file mode 100644
index 000000000000..fa2f89348401
--- /dev/null
+++ b/packages/babel-plugin-transform-classes/test/fixtures/exec/prototype-descriptor.js
@@ -0,0 +1,16 @@
+class A {}
+class B extends A {}
+
+expect(Object.getOwnPropertyDescriptor(A, "prototype")).toEqual({
+  value: A.prototype,
+  configurable: false,
+  enumerable: false,
+  writable: false,
+});
+
+expect(Object.getOwnPropertyDescriptor(B, "prototype")).toEqual({
+  value: B.prototype,
+  configurable: false,
+  enumerable: false,
+  writable: false,
+});