diff --git a/libguile/scmsigs.c b/libguile/scmsigs.c
index 943327303..c4060070b 100644
--- a/libguile/scmsigs.c
+++ b/libguile/scmsigs.c
@@ -108,10 +108,20 @@ static SIGRETTYPE (*orig_handlers[NSIG])(int);
 #endif
 
 static SCM
-close_1 (SCM proc, SCM arg)
+handler_to_async (SCM handler, int signum)
 {
-  return scm_primitive_eval_x (scm_list_3 (scm_sym_lambda, SCM_EOL,
-					   scm_list_2 (proc, arg)));
+  if (scm_is_false (handler))
+    return SCM_BOOL_F;
+  else
+    {
+      SCM async = scm_primitive_eval_x (scm_list_3 (scm_sym_lambda, SCM_EOL,
+						    scm_list_2 (handler,
+								scm_from_int (signum))));
+#if !SCM_USE_PTHREAD_THREADS
+      async = scm_cons (async, SCM_BOOL_F);
+#endif
+      return async;
+    }
 }
 
 #if SCM_USE_PTHREAD_THREADS
@@ -239,23 +249,10 @@ ensure_signal_delivery_thread ()
 #endif /* !SCM_USE_PTHREAD_THREADS */
 
 static void
-install_handler (int signum, SCM thread, SCM handler)
+install_handler (int signum, SCM thread, SCM handler, SCM async)
 {
-  if (scm_is_false (handler))
-    {
-      SCM_SIMPLE_VECTOR_SET (*signal_handlers, signum, SCM_BOOL_F);
-      SCM_SIMPLE_VECTOR_SET (signal_handler_asyncs, signum, SCM_BOOL_F);
-    }
-  else
-    {
-      SCM async = close_1 (handler, scm_from_int (signum));
-#if !SCM_USE_PTHREAD_THREADS
-      async = scm_cons (async, SCM_BOOL_F);
-#endif
-      SCM_SIMPLE_VECTOR_SET (*signal_handlers, signum, handler);
-      SCM_SIMPLE_VECTOR_SET (signal_handler_asyncs, signum, async);
-    }
-
+  SCM_SIMPLE_VECTOR_SET (*signal_handlers, signum, handler);
+  SCM_SIMPLE_VECTOR_SET (signal_handler_asyncs, signum, async);
   SCM_SIMPLE_VECTOR_SET (signal_handler_threads, signum, thread);
 }
 
@@ -308,6 +305,7 @@ SCM_DEFINE (scm_sigaction_for_thread, "sigaction", 1, 3, 0,
   int save_handler = 0;
       
   SCM old_handler;
+  SCM async;
 
   csig = scm_to_signed_integer (signum, 0, NSIG-1);
 
@@ -334,6 +332,10 @@ SCM_DEFINE (scm_sigaction_for_thread, "sigaction", 1, 3, 0,
 	SCM_MISC_ERROR ("thread has already exited", SCM_EOL);
     }
 
+  /* Allocate upfront, as we can't do it inside the critical
+     section. */
+  async = handler_to_async (handler, csig);
+
   ensure_signal_delivery_thread ();
 
   SCM_CRITICAL_SECTION_START;
@@ -351,7 +353,7 @@ SCM_DEFINE (scm_sigaction_for_thread, "sigaction", 1, 3, 0,
 #else
 	  chandler = (SIGRETTYPE (*) (int)) handler_int;
 #endif
-	  install_handler (csig, SCM_BOOL_F, SCM_BOOL_F);
+	  install_handler (csig, SCM_BOOL_F, SCM_BOOL_F, async);
 	}
       else
 	SCM_OUT_OF_RANGE (2, handler);
@@ -366,7 +368,7 @@ SCM_DEFINE (scm_sigaction_for_thread, "sigaction", 1, 3, 0,
 	{
 	  action = orig_handlers[csig];
 	  orig_handlers[csig].sa_handler = SIG_ERR;
-	  install_handler (csig, SCM_BOOL_F, SCM_BOOL_F);
+	  install_handler (csig, SCM_BOOL_F, SCM_BOOL_F, async);
 	}
 #else
       if (orig_handlers[csig] == SIG_ERR)
@@ -375,7 +377,7 @@ SCM_DEFINE (scm_sigaction_for_thread, "sigaction", 1, 3, 0,
 	{
 	  chandler = orig_handlers[csig];
 	  orig_handlers[csig] = SIG_ERR;
-	  install_handler (csig, SCM_BOOL_F, SCM_BOOL_F);
+	  install_handler (csig, SCM_BOOL_F, SCM_BOOL_F, async);
 	}
 #endif
     }
@@ -391,7 +393,7 @@ SCM_DEFINE (scm_sigaction_for_thread, "sigaction", 1, 3, 0,
       if (orig_handlers[csig] == SIG_ERR)
 	save_handler = 1;
 #endif
-      install_handler (csig, thread, handler);
+      install_handler (csig, thread, handler, async);
     }
 
   /* XXX - Silently ignore setting handlers for `program error signals'