diff --git a/build/index.js b/build/index.js
index c54e73f..443a567 100644
--- a/build/index.js
+++ b/build/index.js
@@ -97,8 +97,10 @@ function buildConfig({ manifest: manifestPathRelative, outDir, scriptPlugins = [
     catch (error) {
         throw new Error('Failed to load manifest');
     }
-    const uniqueFileNameSegmentCache = new Map();
-    function uniqueFileNameSegment(filepath, ext = extname(filepath).slice(1)) {
+    // reserve manifest.json at the root of the build output - needs to be the
+    // actual manifest file we generate
+    const uniqueFileNameSegmentCache = new Map([['\0', 'manifest.json']]);
+    function ensureUniquePath(filepath, ext = extname(filepath).slice(1)) {
         // console.log('getting segment for', filepath);
         const cached = uniqueFileNameSegmentCache.get(filepath);
         if (cached) {
@@ -115,18 +117,13 @@ function buildConfig({ manifest: manifestPathRelative, outDir, scriptPlugins = [
         uniqueFileNameSegmentCache.set(filepath, finalName);
         return finalName;
     }
-    function getOutputFilename(entryPath, ext) {
-        // return join(dirname(entryPath), uniqueFileNameSegment(entryPath,
-        // ext));
-        return uniqueFileNameSegment(entryPath, ext);
-    }
     const scripts = getScriptEntrypoints(manifestContent);
     const assets = getAssetEntrypoints(manifestContent);
     return [
         // Process each script entrypoint independently
         ...scripts.map(({ path, replacePath }) => {
             // Figure out where this bundle will live in the output
-            const outPath = getOutputFilename(path, 'js');
+            const outPath = ensureUniquePath(path, 'js');
             // Rewrite the manifest with that path
             replacePath(outPath);
             // Build the bundle
@@ -153,7 +150,7 @@ function buildConfig({ manifest: manifestPathRelative, outDir, scriptPlugins = [
                     buildStart() {
                         assets.forEach(({ path, replacePath }) => {
                             // Figure out where the asset will live in output
-                            const outPath = getOutputFilename(path);
+                            const outPath = ensureUniquePath(path);
                             // Rewrite the manifest with that path
                             replacePath(outPath);
                             // Emit the asset as part of the build step
diff --git a/index.ts b/index.ts
index 43556a1..fc6d518 100644
--- a/index.ts
+++ b/index.ts
@@ -29,8 +29,10 @@ export function buildConfig ({
 		throw new Error('Failed to load manifest');
 	}
 
-	const uniqueFileNameSegmentCache = new Map();
-	function uniqueFileNameSegment (filepath: string, ext = extname(filepath).slice(1)) {
+	// reserve manifest.json at the root of the build output - needs to be the
+	// actual manifest file we generate
+	const uniqueFileNameSegmentCache = new Map([['\0', 'manifest.json']]);
+	function ensureUniquePath (filepath: string, ext = extname(filepath).slice(1)) {
 		// console.log('getting segment for', filepath);
 		const cached = uniqueFileNameSegmentCache.get(filepath);
 		if (cached) {
@@ -51,12 +53,6 @@ export function buildConfig ({
 		return finalName;
 	}
 
-	function getOutputFilename (entryPath: string, ext?: string) {
-		// return join(dirname(entryPath), uniqueFileNameSegment(entryPath,
-		// ext));
-		return uniqueFileNameSegment(entryPath, ext);
-	}
-
 	const scripts = getScriptEntrypoints(manifestContent);
 	const assets = getAssetEntrypoints(manifestContent);
 
@@ -64,7 +60,7 @@ export function buildConfig ({
 		// Process each script entrypoint independently
 		...scripts.map(({path, replacePath}) => {
 			// Figure out where this bundle will live in the output
-			const outPath = getOutputFilename(path, 'js');
+			const outPath = ensureUniquePath(path, 'js');
 
 			// Rewrite the manifest with that path
 			replacePath(outPath);
@@ -94,7 +90,7 @@ export function buildConfig ({
 					buildStart () {
 						assets.forEach(({path, replacePath}) => {
 							// Figure out where the asset will live in output
-							const outPath = getOutputFilename(path);
+							const outPath = ensureUniquePath(path);
 
 							// Rewrite the manifest with that path
 							replacePath(outPath);