diff --git a/configfrag.ac b/configfrag.ac
index 91d737ef..454d9f23 100644
--- a/configfrag.ac
+++ b/configfrag.ac
@@ -46,9 +46,12 @@ AC_DEFINE([BOOTSTRAP_SYMBOLS], [0], [BOOTSTRAP_SYMBOLS])
 # Multiprocessor support is still broken.
 AH_TEMPLATE([MULTIPROCESSOR], [set things up for a uniprocessor])
 mach_ncpus=1
+AC_DEFINE_UNQUOTED([NCPUS], [$mach_ncpus], [number of CPUs])
+
 AC_DEFINE_UNQUOTED([NCPUS], [$mach_ncpus], [number of CPUs])
 [if [ $mach_ncpus -gt 1 ]; then]
   AC_DEFINE([MULTIPROCESSOR], [1], [set things up for a multiprocessor])
+  AC_DEFINE_UNQUOTED([NCPUS], [255], [number of CPUs])
 [fi]
 
 # Restartable Atomic Sequences to get a really fast test-n-set.  Can't be