diff --git a/historic/jam/src/jam.h b/historic/jam/src/jam.h
index 6a7747617..af61c80fa 100644
--- a/historic/jam/src/jam.h
+++ b/historic/jam/src/jam.h
@@ -218,6 +218,7 @@
 
 # ifdef _AIX
 # define unix
+# define MAXLINE 23552 /* 24k - 1k, longest 'together' actions */
 # define OSMINOR "OS=AIX"
 # define OS_AIX
 # define NO_VFORK