diff --git a/Makefile b/Makefile
index ffc9f47..9e417b6 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@ build: dist/build cjs/index.cjs
 
 .PHONY: clean
 clean:
-	rm -r dist/ cjs/
+	rm -rf dist/ cjs/ test/httpwg-tests
 
 .PHONY: test
 test: lint test/httpwg-tests/list.json dist/build
diff --git a/changelog.md b/changelog.md
index f15acbc..6e9369e 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,6 +1,13 @@
 ChangeLog
 =========
 
+2.1.1 (????-??-??)
+------------------
+
+* Fix: serialization of displaystring that encodes to byte values under 0xf,
+  they were missing the 0 padding of %0?.
+
+
 2.1.0 (2026-09-11)
 ------------------
 
diff --git a/src/serializer.ts b/src/serializer.ts
index 27e81d3..88d16f3 100644
--- a/src/serializer.ts
+++ b/src/serializer.ts
@@ -149,7 +149,7 @@ export function serializeDisplayString(input: DisplayString): string {
       || char <= 0x1f
       || char >= 0x7f
     ) {
-      out += '%' + char.toString(16);
+      out += '%' + char.toString(16).padStart(2, '0');
     } else {
       out += String.fromCharCode(char);
     }