diff --git a/pyomo/contrib/iis/mis.py b/pyomo/contrib/iis/mis.py
index 6b6cca8e29c..0141e615516 100644
--- a/pyomo/contrib/iis/mis.py
+++ b/pyomo/contrib/iis/mis.py
@@ -287,7 +287,7 @@ def _constraint_generator():
     except:
         results = None
 
-    if pyo.check_optimal_termination(results):
+    if (results is not None) and pyo.check_optimal_termination(results):
         msg += "Could not determine Minimal Intractable System\n"
     else:
         deletion_filter = []