diff --git a/packages/babel-helper-transform-fixture-test-runner/src/index.js b/packages/babel-helper-transform-fixture-test-runner/src/index.js
index f3b827464e..d5d3b6b847 100644
--- a/packages/babel-helper-transform-fixture-test-runner/src/index.js
+++ b/packages/babel-helper-transform-fixture-test-runner/src/index.js
@@ -33,7 +33,9 @@ testContext.global = testContext;
 runModuleInTestContext("@babel/polyfill", __filename);
 
 // Populate the "babelHelpers" global with Babel's helper utilities.
-runCodeInTestContext(buildExternalHelpers());
+runCodeInTestContext(buildExternalHelpers(), {
+  filename: path.join(__dirname, "babel-helpers-in-memory.js"),
+});
 
 /**
  * A basic implementation of CommonJS so we can execute `@babel/polyfill` inside our test context.
@@ -75,13 +77,10 @@ function runModuleInTestContext(id: string, relativeFilename: string) {
  *
  * Exposed for unit tests, not for use as an API.
  */
-export function runCodeInTestContext(
-  code: string,
-  opts: { filename?: string } = {},
-) {
-  const filename = opts.filename || null;
-  const dirname = filename ? path.dirname(filename) : null;
-  const req = filename ? id => runModuleInTestContext(id, filename) : null;
+export function runCodeInTestContext(code: string, opts: { filename: string }) {
+  const filename = opts.filename;
+  const dirname = path.dirname(filename);
+  const req = id => runModuleInTestContext(id, filename);
 
   const module = {
     id: filename,
diff --git a/packages/babel-helper-transform-fixture-test-runner/test/index.js b/packages/babel-helper-transform-fixture-test-runner/test/index.js
index 05621f4500..2ec3d6bb2c 100644
--- a/packages/babel-helper-transform-fixture-test-runner/test/index.js
+++ b/packages/babel-helper-transform-fixture-test-runner/test/index.js
@@ -4,20 +4,35 @@ describe("helper-transform-fixture-test-runner", function() {
   it("should not execute code in Node's global context", function() {
     try {
       global.foo = "outer";
-      runCodeInTestContext(`
-        expect(global.foo).toBeUndefined();
-        global.foo = "inner";
-      `);
+      runCodeInTestContext(
+        `
+          expect(global.foo).toBeUndefined();
+          global.foo = "inner";
+        `,
+        {
+          filename: `${__filename}.fake1`,
+        },
+      );
 
       expect(global.foo).toBe("outer");
-      runCodeInTestContext(`
-        expect(global.foo).toBe("inner");
-      `);
+      runCodeInTestContext(
+        `
+          expect(global.foo).toBe("inner");
+        `,
+        {
+          filename: `${__filename}.fake2`,
+        },
+      );
     } finally {
       delete global.foo;
-      runCodeInTestContext(`
-        delete global.foo;
-      `);
+      runCodeInTestContext(
+        `
+          delete global.foo;
+        `,
+        {
+          filename: `${__filename}.fake3`,
+        },
+      );
     }
   });
 });