diff --git a/tools/build.py b/tools/build.py
index e66f1f0948..82426f5b26 100755
--- a/tools/build.py
+++ b/tools/build.py
@@ -1,16 +1,27 @@
 #!/usr/bin/env python
 # Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 from __future__ import print_function
+import argparse
 import os
 import sys
 import third_party
 from util import build_path, enable_ansi_colors, run
 
+parser = argparse.ArgumentParser()
+parser.add_argument(
+    "--release", help="Use target/release", action="store_true")
+
 
 def main(argv):
     enable_ansi_colors()
 
-    ninja_args = argv[1:]
+    args, rest_argv = parser.parse_known_args(argv)
+
+    if "DENO_BUILD_MODE" not in os.environ:
+        if args.release:
+            os.environ["DENO_BUILD_MODE"] = "release"
+
+    ninja_args = rest_argv[1:]
     if not "-C" in ninja_args:
         if not os.path.isdir(build_path()):
             print("Build directory '%s' does not exist." % build_path(),
diff --git a/website/manual.md b/website/manual.md
index e5104e6052..8d0dacabca 100644
--- a/website/manual.md
+++ b/website/manual.md
@@ -176,7 +176,7 @@ Extra steps for Windows users:
 ./third_party/depot_tools/ninja -C target/debug
 
 # Build a release binary.
-DENO_BUILD_MODE=release ./tools/build.py :deno
+./tools/build.py --release deno
 
 # List executable targets.
 ./third_party/depot_tools/gn ls target/debug //:* --as=output --type=executable
@@ -622,9 +622,8 @@ To start profiling,
 
 ```sh
 # Make sure we're only building release.
-export DENO_BUILD_MODE=release
 # Build deno and V8's d8.
-./tools/build.py d8 deno
+./tools/build.py --release d8 deno
 # Start the program we want to benchmark with --prof
 ./target/release/deno tests/http_bench.ts --allow-net --prof &
 # Exercise it.