diff --git a/src/build123d/objects_sketch.py b/src/build123d/objects_sketch.py
index 802cd537..62154358 100644
--- a/src/build123d/objects_sketch.py
+++ b/src/build123d/objects_sketch.py
@@ -429,6 +429,13 @@ def __init__(
         self.slot_height = height
 
         half_line = point_v - center_v
+
+        if half_line.length * 2 <= height:
+            raise ValueError(
+                f"Slots must have width > height. "
+                "Got: {height=} width={half_line.length * 2} (computed)"
+            )
+
         face = Face(
             Wire.combine(
                 [