diff --git a/packages/aws-cdk/README.md b/packages/aws-cdk/README.md
index e4566b7bbb690..0a2270b08fc90 100644
--- a/packages/aws-cdk/README.md
+++ b/packages/aws-cdk/README.md
@@ -464,6 +464,7 @@ Some of the interesting keys that can be used in the JSON configuration files:
 ```json5
 {
     "app": "node bin/main.js",        // Command to start the CDK app      (--app='node bin/main.js')
+    "build": "mvn package",           // Specify pre-synth build           (no command line option)
     "context": {                      // Context entries                   (--context=key=value)
         "key": "value"
     },
@@ -473,6 +474,12 @@ Some of the interesting keys that can be used in the JSON configuration files:
 }
 ```
 
+If specified, the command in the `build` key will be executed immediately before synthesis.
+This can be used to build Lambda Functions, CDK Application code, or other assets. 
+`build` cannot be specified on the command line or in the User configuration, 
+and must be specified in the Project configuration. The command specified
+in `build` will be executed by the "watch" process before deployment.
+
 ### Environment
 
 The following environment variables affect aws-cdk:
diff --git a/packages/aws-cdk/lib/api/cxapp/exec.ts b/packages/aws-cdk/lib/api/cxapp/exec.ts
index facaf24a3bfe0..bcc298deaeea2 100644
--- a/packages/aws-cdk/lib/api/cxapp/exec.ts
+++ b/packages/aws-cdk/lib/api/cxapp/exec.ts
@@ -46,6 +46,11 @@ export async function execProgram(aws: SdkProvider, config: Configuration): Prom
   debug('context:', context);
   env[cxapi.CONTEXT_ENV] = JSON.stringify(context);
 
+  const build = config.settings.get(['build']);
+  if (build) {
+    await exec(build);
+  }
+
   const app = config.settings.get(['app']);
   if (!app) {
     throw new Error(`--app is required either in command-line, in ${PROJECT_CONFIG} or in ${USER_DEFAULTS}`);
@@ -74,7 +79,7 @@ export async function execProgram(aws: SdkProvider, config: Configuration): Prom
 
   debug('env:', env);
 
-  await exec();
+  await exec(commandLine.join(' '));
 
   return createAssembly(outdir);
 
@@ -91,7 +96,7 @@ export async function execProgram(aws: SdkProvider, config: Configuration): Prom
     }
   }
 
-  async function exec() {
+  async function exec(commandAndArgs: string) {
     return new Promise<void>((ok, fail) => {
       // We use a slightly lower-level interface to:
       //
@@ -103,7 +108,7 @@ export async function execProgram(aws: SdkProvider, config: Configuration): Prom
       //   anyway, and if the subprocess is printing to it for debugging purposes the
       //   user gets to see it sooner. Plus, capturing doesn't interact nicely with some
       //   processes like Maven.
-      const proc = childProcess.spawn(commandLine[0], commandLine.slice(1), {
+      const proc = childProcess.spawn(commandAndArgs, {
         stdio: ['ignore', 'inherit', 'inherit'],
         detached: false,
         shell: true,
diff --git a/packages/aws-cdk/lib/settings.ts b/packages/aws-cdk/lib/settings.ts
index 4bfafd447d607..6182ecc26e0c3 100644
--- a/packages/aws-cdk/lib/settings.ts
+++ b/packages/aws-cdk/lib/settings.ts
@@ -113,6 +113,10 @@ export class Configuration {
 
     const readUserContext = this.props.readUserContext ?? true;
 
+    if (userConfig.get(['build'])) {
+      throw new Error('The `build` key cannot be specified in the user config (~/.cdk.json), specify it in the project config (cdk.json) instead');
+    }
+
     const contextSources = [
       this.commandLineContext,
       this.projectConfig.subSettings([CONTEXT_KEY]).makeReadOnly(),
diff --git a/packages/aws-cdk/test/api/exec.test.ts b/packages/aws-cdk/test/api/exec.test.ts
index d2e65907527fa..b9c5637acce1a 100644
--- a/packages/aws-cdk/test/api/exec.test.ts
+++ b/packages/aws-cdk/test/api/exec.test.ts
@@ -137,7 +137,7 @@ test('the application set in --app is executed', async () => {
   // GIVEN
   config.settings.set(['app'], 'cloud-executable');
   mockSpawn({
-    commandLine: ['cloud-executable'],
+    commandLine: 'cloud-executable',
     sideEffect: () => writeOutputAssembly(),
   });
 
@@ -149,7 +149,7 @@ test('the application set in --app is executed as-is if it contains a filename t
   // GIVEN
   config.settings.set(['app'], 'does-not-exist');
   mockSpawn({
-    commandLine: ['does-not-exist'],
+    commandLine: 'does-not-exist',
     sideEffect: () => writeOutputAssembly(),
   });
 
@@ -161,7 +161,7 @@ test('the application set in --app is executed with arguments', async () => {
   // GIVEN
   config.settings.set(['app'], 'cloud-executable an-arg');
   mockSpawn({
-    commandLine: ['cloud-executable', 'an-arg'],
+    commandLine: 'cloud-executable an-arg',
     sideEffect: () => writeOutputAssembly(),
   });
 
@@ -174,7 +174,7 @@ test('application set in --app as `*.js` always uses handler on windows', async
   sinon.stub(process, 'platform').value('win32');
   config.settings.set(['app'], 'windows.js');
   mockSpawn({
-    commandLine: [process.execPath, 'windows.js'],
+    commandLine: process.execPath + ' windows.js',
     sideEffect: () => writeOutputAssembly(),
   });
 
@@ -186,7 +186,7 @@ test('application set in --app is `*.js` and executable', async () => {
   // GIVEN
   config.settings.set(['app'], 'executable-app.js');
   mockSpawn({
-    commandLine: ['executable-app.js'],
+    commandLine: 'executable-app.js',
     sideEffect: () => writeOutputAssembly(),
   });
 
@@ -194,6 +194,36 @@ test('application set in --app is `*.js` and executable', async () => {
   await execProgram(sdkProvider, config);
 });
 
+test('cli throws when the `build` script fails', async () => {
+  // GIVEN
+  config.settings.set(['build'], 'fake-command');
+  mockSpawn({
+    commandLine: 'fake-command',
+    exitCode: 127,
+  });
+
+  // WHEN
+  await expect(execProgram(sdkProvider, config)).rejects.toEqual(new Error('Subprocess exited with error 127'));
+}, TEN_SECOND_TIMEOUT);
+
+test('cli does not throw when the `build` script succeeds', async () => {
+  // GIVEN
+  config.settings.set(['build'], 'real command');
+  config.settings.set(['app'], 'executable-app.js');
+  mockSpawn({
+    commandLine: 'real command', // `build` key is not split on whitespace
+    exitCode: 0,
+  },
+  {
+    commandLine: 'executable-app.js',
+    sideEffect: () => writeOutputAssembly(),
+  });
+
+  // WHEN
+  await execProgram(sdkProvider, config);
+}, TEN_SECOND_TIMEOUT);
+
+
 function writeOutputAssembly() {
   const asm = testAssembly({
     stacks: [],
diff --git a/packages/aws-cdk/test/usersettings.test.ts b/packages/aws-cdk/test/usersettings.test.ts
index 948b3b3f907bc..92d7db4a44025 100644
--- a/packages/aws-cdk/test/usersettings.test.ts
+++ b/packages/aws-cdk/test/usersettings.test.ts
@@ -69,4 +69,24 @@ test('load context from all 3 files if available', async () => {
   expect(config.context.get('project')).toBe('foobar');
   expect(config.context.get('foo')).toBe('bar');
   expect(config.context.get('test')).toBe('bar');
+});
+
+test('throws an error if the `build` key is specified in the user config', async () => {
+  // GIVEN
+  const GIVEN_CONFIG: Map<string, any> = new Map([
+    [USER_CONFIG, {
+      build: 'foobar',
+    }],
+  ]);
+
+  // WHEN
+  mockedFs.pathExists.mockImplementation(path => {
+    return GIVEN_CONFIG.has(path);
+  });
+  mockedFs.readJSON.mockImplementation(path => {
+    return GIVEN_CONFIG.get(path);
+  });
+
+  // THEN
+  await expect(new Configuration().load()).rejects.toEqual(new Error('The `build` key cannot be specified in the user config (~/.cdk.json), specify it in the project config (cdk.json) instead'));
 });
\ No newline at end of file
diff --git a/packages/aws-cdk/test/util/mock-child_process.ts b/packages/aws-cdk/test/util/mock-child_process.ts
index 539fd06273399..d7645b4c2ce1a 100644
--- a/packages/aws-cdk/test/util/mock-child_process.ts
+++ b/packages/aws-cdk/test/util/mock-child_process.ts
@@ -6,16 +6,11 @@ if (!(child_process as any).spawn.mockImplementationOnce) {
 }
 
 export interface Invocation {
-  commandLine: string[];
+  commandLine: string;
   cwd?: string;
   exitCode?: number;
   stdout?: string;
 
-  /**
-   * Only match a prefix of the command (don't care about the details of the arguments)
-   */
-  prefix?: boolean;
-
   /**
    * Run this function as a side effect, if present
    */
@@ -26,14 +21,8 @@ export function mockSpawn(...invocations: Invocation[]) {
   let mock = (child_process.spawn as any);
   for (const _invocation of invocations) {
     const invocation = _invocation; // Mirror into variable for closure
-    mock = mock.mockImplementationOnce((binary: string, args: string[], options: child_process.SpawnOptions) => {
-      if (invocation.prefix) {
-        // Match command line prefix
-        expect([binary, ...args].slice(0, invocation.commandLine.length)).toEqual(invocation.commandLine);
-      } else {
-        // Match full command line
-        expect([binary, ...args]).toEqual(invocation.commandLine);
-      }
+    mock = mock.mockImplementationOnce((binary: string, options: child_process.SpawnOptions) => {
+      expect(binary).toEqual(invocation.commandLine);
 
       if (invocation.cwd != null) {
         expect(options.cwd).toBe(invocation.cwd);
@@ -60,8 +49,8 @@ export function mockSpawn(...invocations: Invocation[]) {
     });
   }
 
-  mock.mockImplementation((binary: string, args: string[], _options: any) => {
-    throw new Error(`Did not expect call of ${JSON.stringify([binary, ...args])}`);
+  mock.mockImplementation((binary: string, _options: any) => {
+    throw new Error(`Did not expect call of ${binary}`);
   });
 }