diff -r 83627a092fbf -r d1f060886590 src/Pure/Concurrent/multithreading.scala
--- a/src/Pure/Concurrent/multithreading.scala	Wed Feb 14 15:01:27 2024 +0100
+++ b/src/Pure/Concurrent/multithreading.scala	Wed Feb 14 15:22:21 2024 +0100
@@ -36,7 +36,7 @@
           case _ =>
         }
       }
-      physical_cores.valuesIterator.sum
+      physical_cores.valuesIterator.sum.max(1)
     }