diff --git a/src/lisp/x86-validate-darwin.h b/src/lisp/x86-validate-darwin.h
index 53166e84490afaa1da524cdca64bf7b154b0e362..712a0feb8db1abed28824c9fafa0c33429a62c12 100644
--- a/src/lisp/x86-validate-darwin.h
+++ b/src/lisp/x86-validate-darwin.h
@@ -29,7 +29,9 @@
  */
 #define CONTROL_STACK_SIZE	(0x07fdf000)	/* 128MB - SIGSTKSZ - 1 page */
 
+#if 0
 #define SIGNAL_STACK_START	(0x47fe0000)    /* One page past the end of the control stack */
+#endif
 #define SIGNAL_STACK_SIZE	SIGSTKSZ
 
 #define DYNAMIC_0_SPACE_START	(SpaceStart_TargetDynamic)
diff --git a/src/lisp/x86-validate-linux.h b/src/lisp/x86-validate-linux.h
index 4a0e46cb3d5c43aadedb4c4de4b28f293b63a9b5..258d871870aa451da0de881a62e75082f93086cd 100644
--- a/src/lisp/x86-validate-linux.h
+++ b/src/lisp/x86-validate-linux.h
@@ -42,7 +42,9 @@
 #define CONTROL_STACK_START	0x38000000
 #define CONTROL_STACK_SIZE	(0x07fff000 - 8192)
 
+#if 0
 #define SIGNAL_STACK_START	CONTROL_STACK_END
+#endif
 #define SIGNAL_STACK_SIZE	SIGSTKSZ
 
 #define DYNAMIC_0_SPACE_START	(SpaceStart_TargetDynamic)