diff --git a/src/geouned/GEOUNED/core.py b/src/geouned/GEOUNED/core.py
index 2a2db3ac..4c2d6a31 100644
--- a/src/geouned/GEOUNED/core.py
+++ b/src/geouned/GEOUNED/core.py
@@ -170,6 +170,9 @@ def export_csg(
 
         if not isinstance(UCARD, int) and not isinstance(UCARD, type(None)):
             raise TypeError(f"UCARD should be of type int or None not {type(UCARD)}")
+        if isinstance(UCARD, int):
+            if UCARD < 1:
+                raise ValueError("UCARD should be a positive integer above 1")
 
         for arg, arg_str in (
             (volSDEF, "volSDEF"),