diff --git a/unrouted_handler.go b/unrouted_handler.go
index 2b9411a..dd5acab 100644
--- a/unrouted_handler.go
+++ b/unrouted_handler.go
@@ -459,18 +459,26 @@ func (handler *UnroutedHandler) PatchFile(w http.ResponseWriter, r *http.Request
 		return
 	}
 
-	if handler.composer.UsesLengthDeferrer && info.SizeIsDeferred && r.Header.Get("Upload-Length") != "" {
-		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 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
+				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 {
+			handler.sendError(w, r, ErrNotImplemented)
 		}
 	}