diff --git a/packages/babel-core/src/index.js b/packages/babel-core/src/index.js
index b5ce0fd68067..2a7d05a899da 100644
--- a/packages/babel-core/src/index.js
+++ b/packages/babel-core/src/index.js
@@ -48,6 +48,7 @@ export const DEFAULT_EXTENSIONS = Object.freeze([
   ".es6",
   ".es",
   ".mjs",
+  ".cjs",
 ]);
 
 // For easier backward-compatibility, provide an API like the one we exposed in Babel 6.
diff --git a/packages/babel-register/test/index.js b/packages/babel-register/test/index.js
index 181a768bb8be..6114f61a2a1d 100644
--- a/packages/babel-register/test/index.js
+++ b/packages/babel-register/test/index.js
@@ -41,7 +41,7 @@ jest.mock("source-map-support", () => {
 });
 
 const defaultOptions = {
-  exts: [".js", ".jsx", ".es6", ".es", ".mjs"],
+  exts: [".js", ".jsx", ".es6", ".es", ".mjs", ".cjs"],
   ignoreNodeModules: false,
 };