diff --git a/.gitignore b/.gitignore
index b70cc9f0e6..2080f36b07 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 node_modules/
 .BUILD_COMPLETED
 lerna-debug.log
+tsconfig.tsbuildinfo
 .DS_Store
 .idea
 .vs
diff --git a/packages/codemaker/package.json b/packages/codemaker/package.json
index 83633273f5..a78e24b99f 100644
--- a/packages/codemaker/package.json
+++ b/packages/codemaker/package.json
@@ -5,8 +5,8 @@
   "main": "lib/index.js",
   "types": "lib/index.d.ts",
   "scripts": {
-    "build": "tsc",
-    "watch": "tsc -w",
+    "build": "tsc --build",
+    "watch": "tsc --build -w",
     "test": "nodeunit test/test.*.js",
     "package": "rm -fr dist/js && mkdir -p dist/js && mv $(npm pack) dist/js"
   },
diff --git a/packages/codemaker/tsconfig.json b/packages/codemaker/tsconfig.json
index ad474280a6..ae88dc22ee 100644
--- a/packages/codemaker/tsconfig.json
+++ b/packages/codemaker/tsconfig.json
@@ -12,6 +12,7 @@
     "noUnusedLocals": true,                /* Report errors on unused locals. */
     "noUnusedParameters": true,            /* Report errors on unused parameters. */
     "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
-    "noFallthroughCasesInSwitch": true     /* Report errors for fallthrough cases in switch statement. */
+    "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */
+    "composite": true
   }
 }
diff --git a/packages/jsii-dotnet-jsonmodel/package.json b/packages/jsii-dotnet-jsonmodel/package.json
index 86055ee18e..bc8a691db4 100644
--- a/packages/jsii-dotnet-jsonmodel/package.json
+++ b/packages/jsii-dotnet-jsonmodel/package.json
@@ -7,7 +7,7 @@
   "types": "lib/index.d.ts",
   "scripts": {
     "gen": "/bin/bash ./generate.sh",
-    "build": "tsc && /bin/bash ./build.sh",
+    "build": "tsc --build && /bin/bash ./build.sh",
     "test": "/bin/bash ./test.sh",
     "package": "package-dotnet"
   },
diff --git a/packages/jsii-dotnet-runtime-test/package.json b/packages/jsii-dotnet-runtime-test/package.json
index 4272c4684a..94af26a29c 100644
--- a/packages/jsii-dotnet-runtime-test/package.json
+++ b/packages/jsii-dotnet-runtime-test/package.json
@@ -7,7 +7,7 @@
   "private": true,
   "scripts": {
     "gen": "/bin/bash ./generate.sh",
-    "build": "npm run gen && tsc && /bin/bash ./build.sh",
+    "build": "npm run gen && tsc --build && /bin/bash ./build.sh",
     "test": "/bin/bash ./test.sh"
   },
   "devDependencies": {
diff --git a/packages/jsii-dotnet-runtime/package.json b/packages/jsii-dotnet-runtime/package.json
index 0dd27c95e1..e7749d88b9 100644
--- a/packages/jsii-dotnet-runtime/package.json
+++ b/packages/jsii-dotnet-runtime/package.json
@@ -7,7 +7,7 @@
   "types": "lib/index.d.ts",
   "scripts": {
     "gen": "/bin/bash ./generate.sh",
-    "build": "npm run gen && tsc && /bin/bash ./build.sh",
+    "build": "npm run gen && tsc --build && /bin/bash ./build.sh",
     "test": "/bin/bash ./test.sh",
     "package": "package-dotnet"
   },
diff --git a/packages/jsii-java-runtime/package.json b/packages/jsii-java-runtime/package.json
index 1609887b2c..49f0cac40e 100644
--- a/packages/jsii-java-runtime/package.json
+++ b/packages/jsii-java-runtime/package.json
@@ -7,7 +7,7 @@
   "private": true,
   "scripts": {
     "gen": "/bin/bash ./generate.sh",
-    "build": "tsc && npm run gen && cd project && mvn deploy -D altDeploymentRepository=local::default::file://${PWD}/../maven-repo",
+    "build": "tsc --build && npm run gen && cd project && mvn deploy -D altDeploymentRepository=local::default::file://${PWD}/../maven-repo",
     "test": "echo 'Tests are run as part of the build target'",
     "package": "package-java"
   },
diff --git a/packages/jsii-kernel/package.json b/packages/jsii-kernel/package.json
index dbffb8a582..fb30650756 100644
--- a/packages/jsii-kernel/package.json
+++ b/packages/jsii-kernel/package.json
@@ -5,8 +5,8 @@
   "main": "lib/index.js",
   "types": "lib/index.d.ts",
   "scripts": {
-    "build": "tsc && tslint -p .",
-    "watch": "tsc -w",
+    "build": "tsc --build && tslint -p .",
+    "watch": "tsc --build -w",
     "lint": "tslint -p . --force",
     "test": "nodeunit test/test.*.js",
     "package": "package-js"
diff --git a/packages/jsii-kernel/tsconfig.json b/packages/jsii-kernel/tsconfig.json
index 907de24775..7a4668f0c9 100644
--- a/packages/jsii-kernel/tsconfig.json
+++ b/packages/jsii-kernel/tsconfig.json
@@ -48,7 +48,12 @@
     "inlineSources": true,                    /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
 
     /* Experimental Options */
-    "experimentalDecorators": true            /* Enables experimental support for ES7 decorators. */
+    "experimentalDecorators": true,           /* Enables experimental support for ES7 decorators. */
     // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
-  }
+    "composite": true
+  },
+  "include": ["**/*.ts"],
+  "references": [{
+    "path": "../jsii-spec"
+  }]
 }
diff --git a/packages/jsii-pacmak/package.json b/packages/jsii-pacmak/package.json
index bf011d4964..16926dac54 100644
--- a/packages/jsii-pacmak/package.json
+++ b/packages/jsii-pacmak/package.json
@@ -9,8 +9,8 @@
   "types": "lib/index.d.ts",
   "scripts": {
     "gen": "/bin/bash generate.sh",
-    "build": "npm run gen && tsc && chmod +x bin/jsii-pacmak && tslint -p .",
-    "watch": "tsc -w",
+    "build": "npm run gen && tsc --build && chmod +x bin/jsii-pacmak && tslint -p .",
+    "watch": "tsc --build -w",
     "lint": "tslint -p . --force",
     "test": "/bin/bash test/diff-test.sh && /bin/bash test/build-test.sh",
     "package": "package-js"
diff --git a/packages/jsii-pacmak/tsconfig.json b/packages/jsii-pacmak/tsconfig.json
index 3f968d60b3..d0a9a2d8cc 100644
--- a/packages/jsii-pacmak/tsconfig.json
+++ b/packages/jsii-pacmak/tsconfig.json
@@ -48,7 +48,16 @@
     "inlineSources": true,                   /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
 
     /* Experimental Options */
-    "experimentalDecorators": true            /* Enables experimental support for ES7 decorators. */
+    "experimentalDecorators": true,           /* Enables experimental support for ES7 decorators. */
     // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
-  }
+    "composite": true
+  },
+  "include": [
+    "**/*.ts"
+  ],
+  "references": [{
+    "path": "../jsii-spec"
+  }, {
+    "path": "../codemaker"
+  }]
 }
diff --git a/packages/jsii-reflect/package.json b/packages/jsii-reflect/package.json
index 9273c398f0..365fcd38f5 100644
--- a/packages/jsii-reflect/package.json
+++ b/packages/jsii-reflect/package.json
@@ -8,8 +8,8 @@
     "jsii-tree": "bin/jsii-tree"
   },
   "scripts": {
-    "build": "tsc && chmod +x bin/jsii-tree",
-    "watch": "tsc -w",
+    "build": "tsc --build && chmod +x bin/jsii-tree",
+    "watch": "tsc --build -w",
     "test": "jest",
     "package": "package-js"
   },
diff --git a/packages/jsii-runtime/package.json b/packages/jsii-runtime/package.json
index c171bb54b1..0072bf60db 100644
--- a/packages/jsii-runtime/package.json
+++ b/packages/jsii-runtime/package.json
@@ -8,8 +8,8 @@
     "jsii-runtime": "bin/jsii-runtime"
   },
   "scripts": {
-    "build": "tsc && chmod +x bin/jsii-runtime && /bin/bash ./bundle.sh",
-    "watch": "tsc -w",
+    "build": "tsc --build && chmod +x bin/jsii-runtime && /bin/bash ./bundle.sh",
+    "watch": "tsc --build -w",
     "test": "/bin/bash test/playback-test.sh",
     "package": "package-js"
   },
diff --git a/packages/jsii-spec/lib/spec.ts b/packages/jsii-spec/lib/spec.ts
index cb04ecb2b7..10c5eb0678 100644
--- a/packages/jsii-spec/lib/spec.ts
+++ b/packages/jsii-spec/lib/spec.ts
@@ -161,17 +161,18 @@ export interface PackageVersion {
     dependencies?: { [assembly: string]: PackageVersion };
 
     /**
-     * Indicates if this dependency is a peer dependency or a normal dependency.
+     * Indicates if this dependency is a direct (peer) dependency or a
+     * transitive dependency.
      *
      * Peer dependencies are expected to be explicitly defined by the user of
      * this library instead of brought in as transitive dependencies.
      *
-     * jsii enforces that if this module exports a type from a dependency, this
-     * dependency must be defined as a peer and not as a normal dependency.
-     * Otherwise, it would be impossible to safely use two versions of this
-     * dependency in a closure.
+     * jsii enforces that any direct dependency on another jsii module is also
+     * defined as a peerDependency. Otherwise, it would be impossible to safely
+     * use two versions of this dependency in a closure.
      *
      * @see https://github.com/awslabs/aws-cdk/issues/979
+     * @see https://github.com/awslabs/jsii/issues/361
      * @see https://nodejs.org/en/blog/npm/peer-dependencies/
      */
     peer?: boolean;
diff --git a/packages/jsii-spec/package.json b/packages/jsii-spec/package.json
index 78b37d7979..ffe17dcc2e 100644
--- a/packages/jsii-spec/package.json
+++ b/packages/jsii-spec/package.json
@@ -5,8 +5,8 @@
   "main": "lib/index.js",
   "types": "lib/index.d.ts",
   "scripts": {
-    "watch": "tsc -w",
-    "build": "tsc && bash generate-json-schema.sh",
+    "build": "tsc --build && bash generate-json-schema.sh",
+    "watch": "tsc --build -w",
     "test": "nodeunit test/test.*.js",
     "package": "package-js"
   },
diff --git a/packages/jsii-spec/tsconfig.json b/packages/jsii-spec/tsconfig.json
index 6f8f29cf64..20bcfd995b 100644
--- a/packages/jsii-spec/tsconfig.json
+++ b/packages/jsii-spec/tsconfig.json
@@ -48,7 +48,8 @@
     // "inlineSources": false,                    /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
 
     /* Experimental Options */
-    "experimentalDecorators": true            /* Enables experimental support for ES7 decorators. */
+    "experimentalDecorators": true,           /* Enables experimental support for ES7 decorators. */
     // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
+    "composite": true
   }
 }
diff --git a/packages/jsii/bin/jsii-fix-peers b/packages/jsii/bin/jsii-fix-peers
deleted file mode 100755
index 20df705cb2..0000000000
--- a/packages/jsii/bin/jsii-fix-peers
+++ /dev/null
@@ -1,3 +0,0 @@
-#!/usr/bin/env node
-require('./jsii-fix-peers.js');
-
diff --git a/packages/jsii/bin/jsii-fix-peers.ts b/packages/jsii/bin/jsii-fix-peers.ts
deleted file mode 100644
index 7e2feb7ed4..0000000000
--- a/packages/jsii/bin/jsii-fix-peers.ts
+++ /dev/null
@@ -1,95 +0,0 @@
-//
-// jsii-fix-peers
-//
-// Inspects the local .jsii file and adds "peerDependencies" to the local
-// package.json for all modules that include types that are referenced as part
-// of the current module's public API.
-//
-// This resolves all peer dependency warnings emitted by the jsii compiler.
-//
-
-// tslint:disable:no-console
-
-import fs = require('fs-extra');
-import spec = require('jsii-spec');
-
-fixPeers().catch(e => {
-  console.error(e.stack);
-  process.exit(1);
-});
-
-async function fixPeers() {
-  const jsiiFile = './.jsii';
-  const pkgFile = './package.json';
-
-  if (!(await fs.pathExists(jsiiFile))) {
-    throw new Error(`Cannot find '${jsiiFile}. Make sure to compile first`);
-  }
-
-  if (!(await fs.pathExists(pkgFile))) {
-    throw new Error(`Cannot find '${pkgFile}' in current working directory`);
-  }
-
-  const jsii = await fs.readJson(jsiiFile) as spec.Assembly;
-  const pkg = await fs.readJson(pkgFile);
-
-  // find all type references (FQNs) in the assembly.
-  const fqns = findAllFQNs(jsii);
-
-  let updated = false;
-
-  // read "dependencies" and "peerDependencies" from package.json
-  if (!pkg.peerDependencies) { pkg.peerDependencies = {}; }
-  const peers = pkg.peerDependencies;
-  const deps = pkg.dependencies || {};
-
-  // iterate over all FQNs and ensure that all referenced modules appear as peer dependencies
-  for (const fqn of fqns) {
-    const [ module, ] = fqn.split('.');
-    if (module === jsii.name) {
-      continue;
-    }
-
-    // verify that `module` exists in peerDependencies
-    if (module in peers) {
-      continue;
-    }
-
-    // fetch the module's version requirement from "dependencies" (we expect it to be there)
-    const dep = deps[module];
-    if (!dep) {
-      throw new Error(`Cannot find ${module} neither under "peerDependencies" nor "dependencies". Can't fix.`);
-    }
-
-    // fixing time! add this module to "peerDependencies"
-    peers[module] = dep;
-    console.log(`added ${module}@${dep} to "peerDependencies"`);
-    updated = true;
-  }
-
-  if (updated) {
-    await fs.writeJson(pkgFile, pkg, { spaces: 2 });
-  }
-}
-
-/**
- * Looks up all { "fqn": "boom" } objects in a JSON tree.
- * @param node Initial node (i.e. a JSII assembly)
- * @param out Used by the recursive call to collect outputs
- */
-function findAllFQNs(node: any, out = new Set<string>()) {
-  if (typeof(node) === 'object' && 'fqn' in node) {
-    out.add(node.fqn);
-  }
-
-  for (const key of Object.keys(node)) {
-    const value = node[key];
-    if (Array.isArray(value)) {
-      value.forEach(v => findAllFQNs(v, out));
-    } else if (typeof(value) === 'object') {
-      findAllFQNs(value, out);
-    }
-  }
-
-  return Array.from(out);
-}
diff --git a/packages/jsii/bin/jsii.ts b/packages/jsii/bin/jsii.ts
index efb6a28779..604cae4f9e 100644
--- a/packages/jsii/bin/jsii.ts
+++ b/packages/jsii/bin/jsii.ts
@@ -12,8 +12,16 @@ import { VERSION } from '../lib/version';
         .env('JSII')
         .option('watch', { alias: 'w', type: 'boolean', desc: 'Watch for file changes and recompile automatically' })
         .option('verbose', { alias: 'v', type: 'count', desc: 'Increase the verbosity of output', global: true })
-        // tslint:disable-next-line:max-line-length
-        .option('project-references', { alias: 'r', type: 'boolean', desc: 'Generate TypeScript project references (also [package.json].jsii.projectReferences)' })
+        .option('project-references', {
+            alias: 'r',
+            type: 'boolean',
+            desc: 'Generate TypeScript project references (also [package.json].jsii.projectReferences)'
+        })
+        .option('fix-peer-dependencies', {
+            type: 'boolean',
+            default: true,
+            desc: 'Automatically add missing entries in the peerDependencies section of package.json'
+        })
         .help()
         .version(VERSION)
         .argv;
@@ -23,7 +31,7 @@ import { VERSION } from '../lib/version';
     const projectRoot = path.normalize(path.resolve(process.cwd(), argv._[0] || '.'));
 
     const compiler = new Compiler({
-        projectInfo: await loadProjectInfo(projectRoot),
+        projectInfo: await loadProjectInfo(projectRoot, { fixPeerDependencies: argv['fix-peer-dependencies'] }),
         watch: argv.watch,
         projectReferences: argv['project-references']
     });
diff --git a/packages/jsii/lib/project-info.ts b/packages/jsii/lib/project-info.ts
index 9022f4e1ca..5a3c8a423c 100644
--- a/packages/jsii/lib/project-info.ts
+++ b/packages/jsii/lib/project-info.ts
@@ -39,23 +39,55 @@ export interface ProjectInfo {
     readonly projectReferences?: boolean;
 }
 
-export async function loadProjectInfo(projectRoot: string): Promise<ProjectInfo> {
-    const pkg = require(path.join(projectRoot, 'package.json'));
+export async function loadProjectInfo(projectRoot: string, { fixPeerDependencies }: { fixPeerDependencies: boolean }): Promise<ProjectInfo> {
+    const packageJsonPath = path.join(projectRoot, 'package.json');
+    const pkg = require(packageJsonPath);
 
     const bundleDependencies: { [name: string]: string } = {};
     (pkg.bundleDependencies || pkg.bundledDependencies || []).forEach((name: string) => {
         const version = pkg.dependencies && pkg.dependencies[name];
         if (!version) {
-            throw new Error(`The "package.json" has "${name}" in "bundleDependencies", but it is not declared in "dependencies"`);
+            throw new Error(`The "package.json" file has "${name}" in "bundleDependencies", but it is not declared in "dependencies"`);
         }
 
         if (pkg.peerDependencies && name in pkg.peerDependencies) {
-            throw new Error(`The "package.json" has "${name}" in "bundleDependencies", and also in "peerDependencies"`);
+            throw new Error(`The "package.json" file has "${name}" in "bundleDependencies", and also in "peerDependencies"`);
         }
 
         bundleDependencies[name] = version;
     });
 
+    let addedPeerDependency = false;
+    Object.entries(pkg.dependencies || {}).forEach(([name, version]) => {
+        if (name in bundleDependencies) {
+            return;
+        }
+        pkg.peerDependencies = pkg.peerDependencies || {};
+        const peerVersion = pkg.peerDependencies[name];
+        if (peerVersion === version) {
+            return;
+        }
+        if (!fixPeerDependencies) {
+            if (peerVersion) {
+                // tslint:disable-next-line: max-line-length
+                throw new Error(`The "package.json" file has different version requirements for "${name}" in "dependencies" (${version}) versus "peerDependencies" (${peerVersion})`);
+            }
+            throw new Error(`The "package.json" file has "${name}" in "dependencies", but not in "peerDependencies"`);
+        }
+        if (peerVersion) {
+            LOG.warn(`Changing "peerDependency" on "${name}" from "${peerVersion}" to ${version}`);
+        } else {
+            LOG.warn(`Recording missing "peerDependency" on "${name}" at ${version}`);
+        }
+        pkg.peerDependencies[name] = version;
+        addedPeerDependency = true;
+    });
+    // Re-write "package.json" if we fixed up "peerDependencies" and were told to automatically fix.
+    // Yes, we should never have addedPeerDependencies if not fixPeerDependency, but I still check again.
+    if (addedPeerDependency && fixPeerDependencies) {
+        await fs.writeJson(packageJsonPath, pkg, { encoding: 'utf8', spaces: 2 });
+    }
+
     const transitiveAssemblies: { [name: string]: spec.Assembly } = {};
     const dependencies =
         await _loadDependencies(pkg.dependencies, projectRoot, transitiveAssemblies, new Set<string>(Object.keys(bundleDependencies)));
@@ -109,7 +141,7 @@ function _guessRepositoryType(url: string): string {
     throw new Error(`The "package.json" file must specify the "repository.type" attribute (could not guess from ${url})`);
 }
 
-async function _loadDependencies(dependencies: { [name: string]: string | spec.PackageVersion } | undefined,
+async function _loadDependencies(dependencies: { [name: string]: string | spec.PackageVersion } | undefined,
                                  searchPath: string,
                                  transitiveAssemblies: { [name: string]: spec.Assembly },
                                  bundled = new Set<string>()): Promise<spec.Assembly[]> {
diff --git a/packages/jsii/package.json b/packages/jsii/package.json
index 2c69d2e267..e77d4061f3 100644
--- a/packages/jsii/package.json
+++ b/packages/jsii/package.json
@@ -13,8 +13,8 @@
         "jsii-fix-peers": "bin/jsii-fix-peers"
     },
     "scripts": {
-        "build": "cp ../../README.md . && bash ./generate.sh && tsc",
-        "watch": "bash ./generate.sh && tsc -w",
+        "build": "cp ../../README.md . && bash ./generate.sh && tsc --build",
+        "watch": "bash ./generate.sh && tsc --build -w",
         "test": "nyc nodeunit test/test.*.js",
         "package": "package-js"
     },
diff --git a/packages/jsii/test/test.project-info.ts b/packages/jsii/test/test.project-info.ts
index 534bf7bdb1..4d4a7207a4 100644
--- a/packages/jsii/test/test.project-info.ts
+++ b/packages/jsii/test/test.project-info.ts
@@ -19,7 +19,8 @@ const BASE_PROJECT = {
     jsii: {
         targets: { foo: { bar: 'baz' } }
     },
-    dependencies: { 'jsii-test-dep': '^1.2.3' }
+    dependencies: { 'jsii-test-dep': '^1.2.3' },
+    peerDependencies: { 'jsii-test-dep': '^1.2.3' }
 };
 
 export = nodeunit.testCase({
@@ -27,7 +28,7 @@ export = nodeunit.testCase({
         async 'loads valid project'(test: nodeunit.Test) {
             await _withTestProject(async projectRoot => {
                 try {
-                    const info = await loadProjectInfo(projectRoot);
+                    const info = await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
                     test.equal(info.name, BASE_PROJECT.name);
                     test.equal(info.version, BASE_PROJECT.version);
                     test.equal(info.description, BASE_PROJECT.description);
@@ -52,7 +53,7 @@ export = nodeunit.testCase({
         async 'loads valid project (UNLICENSED)'(test: nodeunit.Test) {
             await _withTestProject(async projectRoot => {
                 try {
-                    const info = await loadProjectInfo(projectRoot);
+                    const info = await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
                     test.equal(info && info.license, 'UNLICENSED');
                 } catch (e) {
                     test.ifError(e);
@@ -67,7 +68,7 @@ export = nodeunit.testCase({
         async 'loads valid project (using bundleDependencies)'(test: nodeunit.Test) {
             await _withTestProject(async projectRoot => {
                 try {
-                    const info = await loadProjectInfo(projectRoot);
+                    const info = await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
                     test.deepEqual(info.bundleDependencies, { bundled: '^1.2.3' });
                 } catch (e) {
                     test.ifError(e);
@@ -83,7 +84,7 @@ export = nodeunit.testCase({
         async 'loads valid project (using bundledDependencies)'(test: nodeunit.Test) {
             await _withTestProject(async projectRoot => {
                 try {
-                    const info = await loadProjectInfo(projectRoot);
+                    const info = await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
                     test.deepEqual(info.bundleDependencies, { bundled: '^1.2.3' });
                 } catch (e) {
                     test.ifError(e);
@@ -100,7 +101,7 @@ export = nodeunit.testCase({
             const contributors = [{ name: 'foo', email: 'nobody@amazon.com' }];
             await _withTestProject(async projectRoot => {
                 try {
-                    const info = await loadProjectInfo(projectRoot);
+                    const info = await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
                     test.deepEqual(info && info.contributors && info.contributors.map(_stripUndefined),
                                    contributors.map(c => ({ ...c, roles: ['contributor'] })));
                 } catch (e) {
@@ -115,7 +116,7 @@ export = nodeunit.testCase({
             await _withTestProject(async projectRoot => {
                 let error: Error | undefined;
                 try {
-                    await loadProjectInfo(projectRoot);
+                    await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
                 } catch (e) {
                     error = e;
                 } finally {
@@ -132,7 +133,7 @@ export = nodeunit.testCase({
             await _withTestProject(async projectRoot => {
                 let error: Error | undefined;
                 try {
-                    await loadProjectInfo(projectRoot);
+                    await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
                 } catch (e) {
                     error = e;
                 } finally {
@@ -149,7 +150,7 @@ export = nodeunit.testCase({
             await _withTestProject(async projectRoot => {
                 let error: Error | undefined;
                 try {
-                    await loadProjectInfo(projectRoot);
+                    await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
                 } catch (e) {
                     error = e;
                 } finally {
@@ -159,8 +160,66 @@ export = nodeunit.testCase({
                 }
             }, info => {
                 info.dependencies[TEST_DEP_ASSEMBLY.name] = '^1.2.5';
+                info.peerDependencies[TEST_DEP_ASSEMBLY.name] = '^1.2.5';
             });
-        }
+        },
+
+        async 'fails to load with missing peerDependency (refusing to auto-fix)'(test: nodeunit.Test) {
+            await _withTestProject(async projectRoot => {
+                let error: Error | undefined;
+                try {
+                    await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
+                } catch (e) {
+                    error = e;
+                } finally {
+                    test.throws(() => { if (error) { throw error; } },
+                                `The "package.json" file has "${TEST_DEP_ASSEMBLY.name}" in "dependencies", but not in "peerDependencies"`);
+                    test.done();
+                }
+            }, info => {
+                delete info.peerDependencies[TEST_DEP_ASSEMBLY.name];
+            });
+        },
+
+        async 'loads with missing peerDependency (when auto-fixing)'(test: nodeunit.Test) {
+            await _withTestProject(async projectRoot => {
+                await loadProjectInfo(projectRoot, { fixPeerDependencies: true });
+                const info = require(path.join(projectRoot, 'package.json'));
+                test.equal(info.peerDependencies[TEST_DEP_ASSEMBLY.name], "^1.2.3");
+                test.done();
+            }, info => {
+                delete info.peerDependencies[TEST_DEP_ASSEMBLY.name];
+            });
+        },
+
+        async 'fails to load with inconsistent peerDependency (refusing to auto-fix)'(test: nodeunit.Test) {
+            await _withTestProject(async projectRoot => {
+                let error: Error | undefined;
+                try {
+                    await loadProjectInfo(projectRoot, { fixPeerDependencies: false });
+                } catch (e) {
+                    error = e;
+                } finally {
+                    test.throws(() => { if (error) { throw error; } },
+                                // tslint:disable-next-line: max-line-length
+                                `The "package.json" file has different version requirements for "${TEST_DEP_ASSEMBLY.name}" in "dependencies" (^1.2.3) versus "peerDependencies" (^42.1337.0)`);
+                    test.done();
+                }
+            }, info => {
+                info.peerDependencies[TEST_DEP_ASSEMBLY.name] = '^42.1337.0';
+            });
+        },
+
+        async 'loads with inconsistent peerDependency (when auto-fixing)'(test: nodeunit.Test) {
+            await _withTestProject(async projectRoot => {
+                await loadProjectInfo(projectRoot, { fixPeerDependencies: true });
+                const info = require(path.join(projectRoot, 'package.json'));
+                test.equal(info.peerDependencies[TEST_DEP_ASSEMBLY.name], "^1.2.3");
+                test.done();
+            }, info => {
+                info.peerDependencies[TEST_DEP_ASSEMBLY.name] = '^42.1337.0';
+            });
+        },
     }
 });
 
@@ -176,7 +235,8 @@ const TEST_DEP_ASSEMBLY: spec.Assembly = {
     fingerprint: 'F1NG3RPR1N7',
     dependencies: {
         'jsii-test-dep-dep': {
-            version: '3.2.1'
+            version: '3.2.1',
+            peer: true,
         }
     },
     jsiiVersion: VERSION,
diff --git a/packages/jsii/tsconfig.json b/packages/jsii/tsconfig.json
index 5bde5dff77..54b8621d79 100644
--- a/packages/jsii/tsconfig.json
+++ b/packages/jsii/tsconfig.json
@@ -16,9 +16,16 @@
     "noFallthroughCasesInSwitch": true,
     "inlineSourceMap": true,
     "inlineSources": true,
-    "experimentalDecorators": true
+    "experimentalDecorators": true,
+    "composite": true
   },
+  "include": [
+    "**/*.ts"
+  ],
   "exclude": [
     "test/negatives/*"
-  ]
+  ],
+  "references": [{
+    "path": "../jsii-spec"
+  }]
 }
diff --git a/packages/oo-ascii-tree/package.json b/packages/oo-ascii-tree/package.json
index c6748b6a7e..9217a1cf93 100644
--- a/packages/oo-ascii-tree/package.json
+++ b/packages/oo-ascii-tree/package.json
@@ -5,8 +5,8 @@
   "main": "lib/index.js",
   "types": "lib/index.d.ts",
   "scripts": {
-    "build": "tsc",
-    "watch": "tsc -w",
+    "build": "tsc --build",
+    "watch": "tsc --build -w",
     "test": "jest",
     "package": "package-js"
   },