diff -up rcs-5.10.0.orig/src/b-isr.c rcs-5.10.0/src/b-isr.c
--- rcs-5.10.0.orig/src/b-isr.c	2021-04-04 14:13:59.185941494 +0200
+++ rcs-5.10.0/src/b-isr.c	2021-04-04 14:15:21.087397267 +0200
@@ -198,22 +198,16 @@ setup_catchsig (size_t count, int const
 #undef MUST
 }
 
-#if defined HAVE_SIGALTSTACK && defined SIGSTKSZ
-#define ISR_STACK_SIZE  (10 * SIGSTKSZ)
-#else
-#define ISR_STACK_SIZE  0
-#endif
-
 struct isr_scratch *
 isr_init (bool *be_quiet)
 {
   struct isr_scratch *scratch = ZLLOC (1, struct isr_scratch);
 
-#if ISR_STACK_SIZE
+#if defined HAVE_SIGALTSTACK && defined SIGSTKSZ
   stack_t ss =
     {
-      .ss_sp = alloc (PLEXUS, ISR_STACK_SIZE),
-      .ss_size = ISR_STACK_SIZE,
+      .ss_sp = alloc (PLEXUS, (10 * SIGSTKSZ)),
+      .ss_size = (10 * SIGSTKSZ),
       .ss_flags = 0
     };