diff --git a/src/mzscheme/src/portfun.c b/src/mzscheme/src/portfun.c
index 6b4ddce556..7ff69d8438 100644
--- a/src/mzscheme/src/portfun.c
+++ b/src/mzscheme/src/portfun.c
@@ -1042,7 +1042,7 @@ static long user_read_result(const char *who, Scheme_Input_Port *port,
       } else if (evt_ok && scheme_is_evt(val)) {
 	/* A peek/read failed, and we were given a evt that unblocks
 	   when the read/peek (at some offset) succeeds. */
-	if (nonblock) {
+	if (nonblock > 0) {
 	  if (sinfo) {
 	    scheme_set_sync_target(sinfo, val, (Scheme_Object *)port, NULL, 0, 1);
 	    return 0;
@@ -1155,6 +1155,7 @@ user_get_or_peek_bytes(Scheme_Input_Port *port,
     fun = uip->read_proc;
 
   while (1) {
+    int nb;
 
     if (uip->reuse_str && (size == SCHEME_BYTE_STRLEN_VAL(uip->reuse_str))) {
       bstr = uip->reuse_str;
@@ -1168,6 +1169,13 @@ user_get_or_peek_bytes(Scheme_Input_Port *port,
     a[1] = peek_skip;
     a[2] = unless ? unless : scheme_false;
 
+    nb = nonblock;
+    if (!nb) {
+      if (scheme_can_break(scheme_current_thread)) {
+	nb = -1;
+      }
+    }
+
     /* Disable breaks while calling the port's function: */
     scheme_push_break_enable(&cframe, 0, 0);
 
@@ -1180,7 +1188,7 @@ user_get_or_peek_bytes(Scheme_Input_Port *port,
     }
 
     r = user_read_result(peek ? "user port peek" : "user port read",
-			 port, val, bstr, peek, nonblock,
+			 port, val, bstr, peek, nb,
 			 1, !!uip->peek_proc, unless && SCHEME_CDR(unless), sinfo);
 
     scheme_pop_break_enable(&cframe, 1);
diff --git a/src/mzscheme/src/sema.c b/src/mzscheme/src/sema.c
index 2696890648..3b8d42f697 100644
--- a/src/mzscheme/src/sema.c
+++ b/src/mzscheme/src/sema.c
@@ -749,6 +749,8 @@ int scheme_wait_semas_chs(int n, Scheme_Object **o, int just_try, Syncing *synci
 		--semas[i]->value;
 	      break;
 	    }
+	  }  else if (semas[i]->so.type == scheme_never_evt_type) {
+	    /* Never ready. */
 	  } else if (try_channel(semas[i], syncing, i, NULL))
 	    break;
 	}
diff --git a/src/mzscheme/src/thread.c b/src/mzscheme/src/thread.c
index 13189c9702..c801b727e6 100644
--- a/src/mzscheme/src/thread.c
+++ b/src/mzscheme/src/thread.c
@@ -5247,21 +5247,23 @@ static Scheme_Object *do_sync(const char *name, int argc, Scheme_Object *argv[],
       if (l) {
 	for (; SCHEME_PAIRP(l); l = SCHEME_CDR(l)) {
 	  a = SCHEME_CAR(l);
+	  if (to_call) {
+	    args[0] = o;
+	    
+	    /* Call wrap proc with breaks disabled */
+	    scheme_push_break_enable(&cframe, 0, 0);
+	    
+	    o = scheme_apply(to_call, 1, args);
+	    
+	    scheme_pop_break_enable(&cframe, 0);
+
+	    to_call = NULL;
+	  }
 	  if (SCHEME_BOXP(a) || SCHEME_PROCP(a)) {
 	    if (SCHEME_BOXP(a)) {
 	      a = SCHEME_BOX_VAL(a);
 	      to_call_is_cont = 1;
 	    }
-	    if (to_call) {
-	      args[0] = o;
-
-	      /* Call wrap proc with breaks disabled */
-	      scheme_push_break_enable(&cframe, 0, 0);
-
-	      o = scheme_apply(to_call, 1, args);
-
-	      scheme_pop_break_enable(&cframe, 0);
-	    }
 	    to_call = a;
 	  } else if (SAME_TYPE(scheme_thread_suspend_type, SCHEME_TYPE(a))
 		     || SAME_TYPE(scheme_thread_resume_type, SCHEME_TYPE(a)))