diff --git a/generate_chip.py b/generate_chip.py
index f73c707..8f08b4f 100644
--- a/generate_chip.py
+++ b/generate_chip.py
@@ -618,7 +618,10 @@ def generate_3d(
     fillet = width * 0.05
     if fillet * 2 >= height:
         fillet = height * 0.2
-    edge = (length - config.gap) / 2
+    gap = config.gap or config.body.gap
+    if gap is None:
+        raise RuntimeError('Generating 3D models not supported for configs without gap')
+    edge = (length - gap) / 2
     translation = (0, 0, height / 2)
     edge_offset = length / 2 - edge