Index: /trunk/ccl/lisp-kernel/thread_manager.c
===================================================================
--- /trunk/ccl/lisp-kernel/thread_manager.c	(revision 5604)
+++ /trunk/ccl/lisp-kernel/thread_manager.c	(revision 5605)
@@ -581,5 +581,7 @@
 #ifdef X86
   tcr->lisp_mxcsr = (1 << MXCSR_DM_BIT) | 
-#if 0
+#if 1                           /* Mask underflow; too hard to 
+                                   deal with denorms if underflow is 
+                                   enabled */
     (1 << MXCSR_UM_BIT) | 
 #endif