diff --git a/pyproject.toml b/pyproject.toml
index 5c06f57e..97d88628 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,7 +26,7 @@ dependencies = [
     "igor2>=0.5.6",
     "iminuit>=2.25.2",
     "joblib>=1.3.2",
-    "lmfit>=1.2.0",
+    "lmfit>=1.2.0, <1.3.0",
     "matplotlib>=3.8.0",
     "numba-progress>=1.0.0",
     "numba>=0.59.0",