diff --git a/.release-notes/set-content-length.md b/.release-notes/set-content-length.md
new file mode 100644
index 0000000..f3309c4
--- /dev/null
+++ b/.release-notes/set-content-length.md
@@ -0,0 +1,3 @@
+## Always set Content-Length
+
+There was a bug where the Content-Length header could end up not being sent. This would cause many clients (such as curl) to hang.
diff --git a/http_server/response.pony b/http_server/response.pony
index 0432370..43cfdc7 100644
--- a/http_server/response.pony
+++ b/http_server/response.pony
@@ -298,8 +298,8 @@ class val BuildableResponse is (Response & ByteSeqIter)
     match cl
     | let clu: USize =>
       set_header("Content-Length", cl.string())
-    // | None =>
-    // TODO: drop header
+    | None =>
+      set_header("Content-Length", "0")
     end
     this