diff --git a/src/pymatgen/io/vasp/inputs.py b/src/pymatgen/io/vasp/inputs.py
index 07bff38a14a..6fa0f690df2 100644
--- a/src/pymatgen/io/vasp/inputs.py
+++ b/src/pymatgen/io/vasp/inputs.py
@@ -970,6 +970,7 @@ def proc_val(key: str, val: str) -> list | bool | float | int | str:
             "PARAM1",
             "PARAM2",
             "ENCUT",
+            "NUPDOWN",
         )
         int_keys = (
             "NSW",
@@ -987,7 +988,6 @@ def proc_val(key: str, val: str) -> list | bool | float | int | str:
             "LMAXMIX",
             "NSIM",
             "NKRED",
-            "NUPDOWN",
             "ISPIND",
             "LDAUTYPE",
             "IVDW",