diff --git a/rest_api/pyproject.toml b/rest_api/pyproject.toml
index eac58f7fd..cd65bc1ae 100644
--- a/rest_api/pyproject.toml
+++ b/rest_api/pyproject.toml
@@ -26,7 +26,7 @@ classifiers = [
 ]
 dependencies = [
     "farm-haystack",
-    "fastapi<1",
+    "fastapi<0.104.0",  # https://github.com/deepset-ai/haystack/issues/6119
     "uvicorn<1",
     "python-multipart<1",  # optional FastAPI dependency for form data
     "pynvml",