diff --git a/packages/autobuild/autotools/tangram.ts b/packages/autobuild/autotools/tangram.ts
index b07bc281..230c3c41 100644
--- a/packages/autobuild/autotools/tangram.ts
+++ b/packages/autobuild/autotools/tangram.ts
@@ -16,10 +16,10 @@ export type Arg = {
 };
 
 export const build = tg.target(async (arg: Arg) => {
-	const { build, env: envArg, host, source } = arg ?? {};
+	const { env: envArg, ...rest } = arg ?? {};
 
-	const env_ = envArg ?? env({ build, host });
-	const arg_ = { build, env: env_, host, source };
+	const env_ = envArg ?? env({ build: arg.build, host: arg.host });
+	const arg_ = { ...rest, env: env_ };
 	return std.autotools.build(arg_);
 });
 
diff --git a/packages/autobuild/cmake/tangram.ts b/packages/autobuild/cmake/tangram.ts
index 2c5e228d..dfbe8000 100644
--- a/packages/autobuild/cmake/tangram.ts
+++ b/packages/autobuild/cmake/tangram.ts
@@ -9,10 +9,11 @@ export type Arg = {
 };
 
 export const build = tg.target(async (arg: Arg) => {
-	const { build, env: envArg, host, source } = arg ?? {};
+	const { env: envArg, ...rest } = arg ?? {};
 
-	const env_ = envArg ?? std.env.arg(env({ build, host }), envArg);
-	const arg_ = { build, env: env_, host, source };
+	const env_ =
+		envArg ?? std.env.arg(env({ build: arg.build, host: arg.host }), envArg);
+	const arg_ = { ...rest, env: env_ };
 
 	return cmake.build(arg_);
 });
diff --git a/packages/autobuild/go/tangram.ts b/packages/autobuild/go/tangram.ts
index 0f46a168..6a04720a 100644
--- a/packages/autobuild/go/tangram.ts
+++ b/packages/autobuild/go/tangram.ts
@@ -9,10 +9,10 @@ export type Arg = {
 };
 
 export const build = tg.target(async (arg: Arg) => {
-	const { build, env: envArg, host, source } = arg ?? {};
+	const { env: envArg, ...rest } = arg ?? {};
 
-	const env_ = envArg ?? env({ build, host });
-	const arg_ = { build, env: env_, host, source };
+	const env_ = envArg ?? env({ build: arg.build, host: arg.host });
+	const arg_ = { ...rest, env: env_ };
 	return go.build(arg_);
 });
 
diff --git a/packages/autobuild/python/tangram.ts b/packages/autobuild/python/tangram.ts
index 2517ccda..017a883d 100644
--- a/packages/autobuild/python/tangram.ts
+++ b/packages/autobuild/python/tangram.ts
@@ -11,15 +11,17 @@ export type Arg = {
 };
 
 export const build = tg.target(async (arg: Arg) => {
-	const { build, env: envArg, host, source } = arg ?? {};
+	const { env: envArg, source, ...rest } = arg ?? {};
 
-	const env_ = envArg ?? std.env.arg(env({ build, host }), envArg);
-	let arg_: python.BuildArg = { build, env: env_, host, source };
+	const env_ =
+		envArg ??
+		(await std.env.arg(env({ build: arg.build, host: arg.host }), envArg));
+	let arg_: python.BuildArg = { ...rest, env: env_, source };
 
 	const maybeRequirements = source.tryGet("requirements.txt");
 	if (maybeRequirements) {
 		if (maybeRequirements instanceof tg.File) {
-			arg_ = { ...arg_, requirements: maybeRequirements };
+			arg_ = { ...arg_, python: { requirements: maybeRequirements } };
 		}
 	}
 
@@ -38,7 +40,7 @@ export const plain = tg.target(async (arg: Arg) => {
 		directory: source,
 		extension: ".py",
 		interpreter,
-		env: std.env.arg(
+		env: await std.env.arg(
 			{
 				PYTHONPATH: toolchain,
 			},
@@ -56,11 +58,13 @@ export const plain = tg.target(async (arg: Arg) => {
 // });
 
 export const pyproject = tg.target(async (arg: Arg) => {
-	const { build, env: envArg, host, source } = arg ?? {};
+	const { env: envArg, source, ...rest } = arg ?? {};
 
-	const env_ = envArg ?? std.env.arg(env({ build, host }), envArg);
+	const env_ =
+		envArg ??
+		(await std.env.arg(env({ build: arg.build, host: arg.host }), envArg));
 	const pyprojectToml = await source.get("pyproject.toml").then(tg.File.expect);
-	const arg_ = { build, env: env_, host, pyprojectToml, source };
+	const arg_ = { ...rest, env: env_, pyprojectToml, source };
 	return python.build(arg_);
 });
 
diff --git a/packages/autobuild/ruby/tangram.ts b/packages/autobuild/ruby/tangram.ts
index 8dee17e2..f6cadcba 100644
--- a/packages/autobuild/ruby/tangram.ts
+++ b/packages/autobuild/ruby/tangram.ts
@@ -10,9 +10,11 @@ export type Arg = {
 };
 
 export const plain = tg.target(async (arg: Arg) => {
-	const { build, env: envArg, host, source } = arg ?? {};
+	const { env: envArg, source } = arg ?? {};
 
-	const env_ = envArg ?? std.env.arg(env({ build, host }), envArg);
+	const env_ =
+		envArg ??
+		(await std.env.arg(env({ build: arg.build, host: arg.host }), envArg));
 	const toolchain = await ruby.toolchain();
 	const interpreter = await toolchain.get("bin/ruby").then(tg.File.expect);
 	return wrapScripts({
diff --git a/packages/autobuild/rust/tangram.ts b/packages/autobuild/rust/tangram.ts
index 9d4d921c..ba1d910b 100644
--- a/packages/autobuild/rust/tangram.ts
+++ b/packages/autobuild/rust/tangram.ts
@@ -11,10 +11,11 @@ export type Arg = {
 };
 
 export const cargo = tg.target(async (arg: Arg) => {
-	const { build, env: envArg, host, source } = arg ?? {};
+	const { env: envArg, ...rest } = arg ?? {};
 
-	const env_ = envArg ?? std.env.arg(env({ build, host }), envArg);
-	const arg_ = { build, env: env_, host, source };
+	const env_ =
+		envArg ?? std.env.arg(env({ build: arg.build, host: arg.host }), envArg);
+	const arg_ = { ...rest, env: env_ };
 
 	return await rust.cargo.build(arg_);
 });
@@ -22,10 +23,10 @@ export const cargo = tg.target(async (arg: Arg) => {
 export default cargo;
 
 export const plain = tg.target(async (arg: Arg) => {
-	const { build, env: envArg, host, source } = arg ?? {};
+	const { env: envArg, ...rest } = arg ?? {};
 
-	const env_ = envArg ?? env({ build, host });
-	const arg_ = { build, env: env_, host, source };
+	const env_ = envArg ?? env({ build: arg.build, host: arg.host });
+	const arg_ = { ...rest, env: env_ };
 
 	return await rust.build.build(arg_);
 });
diff --git a/packages/python/tangram.ts b/packages/python/tangram.ts
index b6fd0714..7020ee43 100644
--- a/packages/python/tangram.ts
+++ b/packages/python/tangram.ts
@@ -342,6 +342,9 @@ export type BuildArg = {
 	/** The machine this package will build on. */
 	build?: string;
 
+	/** Additi8onal environment to include. */
+	env?: std.env.Arg;
+
 	/** The machine this package produces binaries for. */
 	host?: string;
 
@@ -361,6 +364,7 @@ export const build = tg.target(async (...args: std.Args<BuildArg>) => {
 	);
 	const {
 		build: buildTriple_,
+		env,
 		host: host_,
 		python: pythonArg,
 		pyprojectToml: pyprojectToml_,
@@ -387,7 +391,7 @@ export const build = tg.target(async (...args: std.Args<BuildArg>) => {
 
 	// Construct the python environment.
 	const pythonArtifact = await tg.directory(
-		toolchain({ ...pythonArg, build: buildTriple, host }),
+		toolchain({ ...pythonArg, build: buildTriple, env, host }),
 		{
 			["lib/python3/site-packages"]: {
 				[name]: tg.symlink(tg`${source}/src/${name}`),