diff --git a/cors_test.go b/cors_test.go
index e7876e5..fd56f80 100644
--- a/cors_test.go
+++ b/cors_test.go
@@ -21,7 +21,7 @@ func TestCORS(t *testing.T) {
 			},
 			Code: http.StatusOK,
 			ResHeader: map[string]string{
-				"Access-Control-Allow-Headers": "Origin, X-Requested-With, Content-Type, Upload-Length, Upload-Offset, Tus-Resumable, Upload-Metadata",
+				"Access-Control-Allow-Headers": "Origin, X-Requested-With, Content-Type, Upload-Length, Upload-Offset, Tus-Resumable, Upload-Metadata, Upload-Defer-Length",
 				"Access-Control-Allow-Methods": "POST, GET, HEAD, PATCH, DELETE, OPTIONS",
 				"Access-Control-Max-Age":       "86400",
 				"Access-Control-Allow-Origin":  "tus.io",
@@ -42,7 +42,7 @@ func TestCORS(t *testing.T) {
 			},
 			Code: http.StatusMethodNotAllowed,
 			ResHeader: map[string]string{
-				"Access-Control-Expose-Headers": "Upload-Offset, Location, Upload-Length, Tus-Version, Tus-Resumable, Tus-Max-Size, Tus-Extension, Upload-Metadata",
+				"Access-Control-Expose-Headers": "Upload-Offset, Location, Upload-Length, Tus-Version, Tus-Resumable, Tus-Max-Size, Tus-Extension, Upload-Metadata, Upload-Defer-Length",
 				"Access-Control-Allow-Origin":   "tus.io",
 			},
 		}).Run(handler, t)
diff --git a/unrouted_handler.go b/unrouted_handler.go
index 4cc4e23..ae283d3 100644
--- a/unrouted_handler.go
+++ b/unrouted_handler.go
@@ -174,12 +174,12 @@ func (handler *UnroutedHandler) Middleware(h http.Handler) http.Handler {
 			if r.Method == "OPTIONS" {
 				// Preflight request
 				header.Add("Access-Control-Allow-Methods", "POST, GET, HEAD, PATCH, DELETE, OPTIONS")
-				header.Add("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Upload-Length, Upload-Offset, Tus-Resumable, Upload-Metadata")
+				header.Add("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Upload-Length, Upload-Offset, Tus-Resumable, Upload-Metadata, Upload-Defer-Length")
 				header.Set("Access-Control-Max-Age", "86400")
 
 			} else {
 				// Actual request
-				header.Add("Access-Control-Expose-Headers", "Upload-Offset, Location, Upload-Length, Tus-Version, Tus-Resumable, Tus-Max-Size, Tus-Extension, Upload-Metadata")
+				header.Add("Access-Control-Expose-Headers", "Upload-Offset, Location, Upload-Length, Tus-Version, Tus-Resumable, Tus-Max-Size, Tus-Extension, Upload-Metadata, Upload-Defer-Length")
 			}
 		}
 
@@ -461,26 +461,26 @@ func (handler *UnroutedHandler) PatchFile(w http.ResponseWriter, r *http.Request
 	}
 
 	if r.Header.Get("Upload-Length") != "" {
-		if handler.composer.UsesLengthDeferrer {
-			if info.SizeIsDeferred {
-				uploadLength, err := strconv.ParseInt(r.Header.Get("Upload-Length"), 10, 64)
-				if err != nil || uploadLength < 0 || uploadLength < info.Offset || uploadLength > handler.config.MaxSize {
-					handler.sendError(w, r, ErrInvalidUploadLength)
-					return
-				}
-
-				info.Size = uploadLength
-				info.SizeIsDeferred = false
-				if err := handler.composer.LengthDeferrer.DeclareLength(id, info.Size); err != nil {
-					handler.sendError(w, r, err)
-					return
-				}
-			} else {
-				handler.sendError(w, r, ErrInvalidUploadLength)
-			}
-		} else {
+		if !handler.composer.UsesLengthDeferrer {
 			handler.sendError(w, r, ErrNotImplemented)
+			return
 		}
+		if !info.SizeIsDeferred {
+			handler.sendError(w, r, ErrInvalidUploadLength)
+			return
+		}
+		uploadLength, err := strconv.ParseInt(r.Header.Get("Upload-Length"), 10, 64)
+		if err != nil || uploadLength < 0 || uploadLength < info.Offset || uploadLength > handler.config.MaxSize {
+			handler.sendError(w, r, ErrInvalidUploadLength)
+			return
+		}
+		if err := handler.composer.LengthDeferrer.DeclareLength(id, uploadLength); err != nil {
+			handler.sendError(w, r, err)
+			return
+		}
+
+		info.Size = uploadLength
+		info.SizeIsDeferred = false
 	}
 
 	if err := handler.writeChunk(id, info, w, r); err != nil {