diff --git a/colmena/models.py b/colmena/models.py
index 2773a19..383a35b 100644
--- a/colmena/models.py
+++ b/colmena/models.py
@@ -317,7 +317,7 @@ def mark_compute_ended(self):
         """Mark when the task finished executing"""
         self.timestamp.compute_ended = datetime.now().timestamp()
 
-    def set_result(self, result: Any, runtime: float = None):
+    def set_result(self, result: Any, runtime: float = nan):
         """Set the value of this computation
 
         Automatically sets the "time_result_completed" field and, if known, defines the runtime.