diff --git a/lib/middleware/serveThemes.js b/lib/middleware/serveThemes.js
index 15dfc131..6cce31a0 100644
--- a/lib/middleware/serveThemes.js
+++ b/lib/middleware/serveThemes.js
@@ -39,48 +39,48 @@ function createMiddleware({resources}) {
 		fs: fsInterface(resources.all)
 	});
 
-	return function theme(req, res, next) {
-		const pathname = parseurl(req).pathname;
-		const filename = basename(pathname);
-		if (!themeResources.includes(filename)) {
-			next();
-			return;
-		}
+	return async function theme(req, res, next) {
+		try {
+			const pathname = parseurl(req).pathname;
+			const filename = basename(pathname);
+			if (!themeResources.includes(filename)) {
+				next();
+				return;
+			}
 
-		const sourceLessPath = dirname(pathname) + "/library.source.less";
-		resources.all.byPath(sourceLessPath).then((sourceLessResource) => {
+			const sourceLessPath = dirname(pathname) + "/library.source.less";
+			const sourceLessResource = await resources.all.byPath(sourceLessPath);
 			if (!sourceLessResource) { // Not found
 				next();
 				return;
 			}
-			return builder.build([sourceLessResource]).then(function(createdResources) {
-				// Pick requested file resource
-				const resource = createdResources.find((res) => res.getPath().endsWith(filename));
-				if (!resource) {
-					next(new Error(`Theme Build did not return request file "${pathname}"`));
-					return;
-				}
 
-				const resourcePath = resource.getPath();
-				const {contentType} = getMimeInfo(resourcePath);
-				res.setHeader("Content-Type", contentType);
+			const createdResources = await builder.build([sourceLessResource]);
+			// Pick requested file resource
+			const resource = createdResources.find((res) => res.getPath().endsWith(filename));
+			if (!resource) {
+				next(new Error(`Theme Build did not return request file "${pathname}"`));
+				return;
+			}
+
+			const resourcePath = resource.getPath();
+			const {contentType} = getMimeInfo(resourcePath);
+			res.setHeader("Content-Type", contentType);
 
-				return resource.getBuffer().then((content) => {
-					res.setHeader("ETag", etag(content));
+			const content = await resource.getBuffer();
+			res.setHeader("ETag", etag(content));
 
-					if (isFresh(req, res)) {
-						// client has a fresh copy of the resource
-						res.statusCode = 304;
-						res.end();
-						return;
-					}
+			if (isFresh(req, res)) {
+				// client has a fresh copy of the resource
+				res.statusCode = 304;
+				res.end();
+				return;
+			}
 
-					res.end(content.toString());
-				});
-			});
-		}).catch(function(err) {
+			res.end(content.toString());
+		} catch (err) {
 			next(err);
-		});
+		}
 	};
 }
 
diff --git a/test/lib/server/middleware/serveThemes.js b/test/lib/server/middleware/serveThemes.js
index 37088133..ca0a37e6 100644
--- a/test/lib/server/middleware/serveThemes.js
+++ b/test/lib/server/middleware/serveThemes.js
@@ -258,3 +258,22 @@ test.serial.cb("Error handling: Request resource that ThemeBuild doesn't return"
 		t.end();
 	});
 });
+
+test.serial.cb("Error handling: Unexpected exception within middleware should call next with error", (t) => {
+	const error = new Error("Unexpected Error");
+
+	const {middleware, byPath} = createMiddleware();
+	byPath.rejects(error);
+
+	const req = {
+		url: "/resources/sap/ui/test/themes/base/library.css",
+		headers: {}
+	};
+
+	const res = {};
+
+	middleware(req, res, function(err) {
+		t.is(err, error);
+		t.end();
+	});
+});