diff --git a/packages/esbuild/esbuild.bzl b/packages/esbuild/esbuild.bzl
index bbcf5c792e..255f4ca8cf 100644
--- a/packages/esbuild/esbuild.bzl
+++ b/packages/esbuild/esbuild.bzl
@@ -50,7 +50,7 @@ def _esbuild_impl(ctx):
     args.add_joined(["--log-level", "info"], join_with = "=")
     args.add_joined(["--metafile", metafile.path], join_with = "=")
     args.add_all(ctx.attr.define, format_each = "--define:%s")
-    args.add_all(ctx.attr.external, format_each = "--external=%s")
+    args.add_all(ctx.attr.external, format_each = "--external:%s")
 
     # disable the error limit and show all errors
     args.add_joined(["--error-limit", "0"], join_with = "=")
diff --git a/packages/esbuild/test/external-flag/BUILD.bazel b/packages/esbuild/test/external-flag/BUILD.bazel
new file mode 100644
index 0000000000..886a80397e
--- /dev/null
+++ b/packages/esbuild/test/external-flag/BUILD.bazel
@@ -0,0 +1,28 @@
+load("//packages/esbuild/test:tests.bzl", "esbuild")
+load("//packages/jasmine:index.bzl", "jasmine_node_test")
+load("//packages/typescript:index.bzl", "ts_library")
+
+ts_library(
+    name = "main",
+    srcs = [
+        "main.ts",
+    ],
+    deps = [
+        "@npm//@types/node",
+    ],
+)
+
+esbuild(
+    name = "bundle",
+    entry_point = "main.ts",
+    external = [
+        "fs",
+    ],
+    deps = [":main"],
+)
+
+jasmine_node_test(
+    name = "bundle_test",
+    srcs = ["bundle_test.js"],
+    data = [":bundle"],
+)
diff --git a/packages/esbuild/test/external-flag/bundle_test.js b/packages/esbuild/test/external-flag/bundle_test.js
new file mode 100644
index 0000000000..0770e66d7e
--- /dev/null
+++ b/packages/esbuild/test/external-flag/bundle_test.js
@@ -0,0 +1,12 @@
+const {readFileSync} = require('fs');
+
+const helper = require(process.env.BAZEL_NODE_RUNFILES_HELPER);
+const location =
+    helper.resolve('build_bazel_rules_nodejs/packages/esbuild/test/external-flag/bundle.js');
+
+describe('esbuild external-flag', () => {
+  it('compiles with the external module \'fs\'', () => {
+    const bundle = readFileSync(location, {encoding: 'utf8'});
+    expect(bundle).toContain('console.log(fs)');
+  });
+})
diff --git a/packages/esbuild/test/external-flag/main.ts b/packages/esbuild/test/external-flag/main.ts
new file mode 100644
index 0000000000..8f2042b9b0
--- /dev/null
+++ b/packages/esbuild/test/external-flag/main.ts
@@ -0,0 +1,4 @@
+import * as fs from 'fs';
+
+// Prevent 'fs' from being tree-shaken.
+console.log(fs);