diff --git a/islpy/__init__.py b/islpy/__init__.py
index 7998b2e481f3e916305c35b5a262f446b3ebae6f..ead93f2be4b223c7b1977ff58b7272af05c3ae14 100644
--- a/islpy/__init__.py
+++ b/islpy/__init__.py
@@ -130,6 +130,9 @@ EXPR_CLASSES = tuple(cls for cls in ALL_CLASSES
 
 
 def _runs_in_integer_set(s, max_int=None):
+    if not s:
+        return
+
     if max_int is None:
         max_int = max(s)