diff --git a/prjxray/segmaker.py b/prjxray/segmaker.py
index 65cb78b9..78fa8f53 100644
--- a/prjxray/segmaker.py
+++ b/prjxray/segmaker.py
@@ -80,6 +80,7 @@ class Segmaker:
         self.part = part
         if self.part is None:
             self.part = util.get_part()
+            assert self.part, "No part specified."
 
         self.verbose = verbose if verbose is not None else os.getenv(
             'VERBOSE', 'N') == 'Y'
diff --git a/prjxray/util.py b/prjxray/util.py
index ff2c7bf1..8fa737f6 100644
--- a/prjxray/util.py
+++ b/prjxray/util.py
@@ -17,7 +17,6 @@ def get_db_root():
 
 def get_part():
     ret = os.getenv("XRAY_PART", None)
-    assert ret
 
     return ret