diff --git a/lib/register.js b/lib/register.js
index 9b72e624..29935cf9 100644
--- a/lib/register.js
+++ b/lib/register.js
@@ -5,6 +5,10 @@
  * to insert tracking code.
  * ------------------*/
 
+/* eeslint-disable import/no-extraneous-dependencies */
+/* eeslint-disable node/no-extraneous-require */
+/* eslint-disable global-require */
+
 'use strict';
 
 // Catalog globals etc
@@ -120,10 +124,22 @@ function register(options) {
 		}
 	});
 
+	const {dirname, join: pathJoin, sep: pathSep} = require('path'),
+		{writeFileSync} = require('fs'),
+		{ensureDirSync} = require('fs-extra');
+	const rootDir = pathJoin(__dirname, '..', pathSep);
+
 	// Add pirates hook to capture code post-babel
 	if (piratesRevert) piratesRevert();
 	piratesRevert = addHook((code, filename) => {
 		transpiledFiles[filename] = parseSourceMapFromCode(code);
+
+		if (filename.startsWith(rootDir)) {
+			const writePath = pathJoin(rootDir, 'example/intermediate', filename.slice(rootDir.length));
+			ensureDirSync(dirname(writePath));
+			writeFileSync(writePath, code);
+		}
+
 		return code;
 	}, {ignoreNodeModules: false});
 }
diff --git a/lib/serialize/records.js b/lib/serialize/records.js
index 56c53c25..253e5e14 100644
--- a/lib/serialize/records.js
+++ b/lib/serialize/records.js
@@ -125,6 +125,12 @@ function updateBlockParent(block, parent) {
 	}
 }
 
+// TODO Delete this
+function traceBlock(name, block) {
+	console.log(`${name}.id:`, block.id); // eslint-disable-line no-console
+	if (block.parent) traceBlock(`${name}.parent`, block.parent); // eslint-disable-line no-unused-vars
+}
+
 /**
  * Create scope object
  * @param {number} [id] - Scope ID
@@ -178,6 +184,12 @@ function updateScopeParent(scope, parent) {
 	}
 }
 
+// TODO Delete this
+function traceScope(name, scope) {
+	console.log(`${name}.block.id:`, scope.block.id); // eslint-disable-line no-console
+	if (scope.parent) traceScope(`${name}.parent`, scope.parent); // eslint-disable-line no-unused-vars
+}
+
 /**
  * Create dependency relationship between two values.
  * @param {Object} srcRecord - Record for value which depends on the other
diff --git a/lib/serialize/serializer.js b/lib/serialize/serializer.js
index 784d4dce..6fadf1ba 100644
--- a/lib/serialize/serializer.js
+++ b/lib/serialize/serializer.js
@@ -225,6 +225,40 @@ class Serializer {
 			importNodes = [],
 			{mangle} = this.options;
 
+		/*
+		// TODO Delete this
+		const found = new Set();
+		function findCircularDependency(record, stack) { // eslint-disable-line no-shadow
+			if (found.has(record)) return;
+
+			const newStack = new Set(stack);
+			newStack.add(record);
+			// console.log('stack:', [...newStack].map(rec => rec.varNode.name));
+
+			if (stack.has(record)) {
+				// eslint-disable-next-line no-console
+				console.log('circular:', [...newStack].map(rec => rec.varNode.name));
+				process.exit(); // eslint-disable-line no-process-exit
+			}
+
+			for (const dependency of record.dependencies) {
+				findCircularDependency(dependency.record, newStack);
+			}
+
+			found.add(record);
+
+			if (record.assignments) {
+				for (const assignment of record.assignments) {
+					for (const dependency of assignment.dependencies) {
+						findCircularDependency(dependency.record, new Set());
+					}
+				}
+			}
+		}
+
+		findCircularDependency(record, new Set());
+		*/
+
 		const queue = [record],
 			processing = new Map(); // Keyed by record, values = `true` for processed, `false` for processing
 		function processQueue() {
diff --git a/validateSourcemaps.js b/validateSourcemaps.js
new file mode 100644
index 00000000..c7a34f5b
--- /dev/null
+++ b/validateSourcemaps.js
@@ -0,0 +1,41 @@
+/* eslint-disable no-console */
+
+'use strict';
+
+const pathJoin = require('path').join,
+	{readFile} = require('fs').promises, // eslint-disable-line node/no-unsupported-features/node-builtins
+	readdir = require('recursive-readdir'),
+	validate = require('sourcemap-validator');
+
+const dirPath = pathJoin(__dirname, 'example/intermediate/example');
+// const dirPath = pathJoin(__dirname, 'node_modules/is-it-type/dist');
+
+(async () => {
+	const paths = await readdir(dirPath);
+
+	for (const path of paths) {
+		if (!path.match(/\.js$/)) continue;
+
+		const code = await readFile(path, 'utf8');
+
+		let map;
+		const mapPath = `${path}.map`;
+		try {
+			map = await readFile(mapPath, 'utf8');
+		} catch (err) {} // eslint-disable-line no-empty
+
+		const pathShort = path.slice(dirPath.length);
+
+		try {
+			validate(code, map);
+			console.log('VALID:', pathShort);
+		} catch (err) {
+			if (err.message === 'No map argument provided, and no inline sourcemap found') {
+				console.log('NO SOURCE MAP:', pathShort);
+			} else {
+				console.log('INVALID:', pathShort, err.message);
+			}
+			// console.log(path, err.message);
+		}
+	}
+})();