diff --git a/GNUmakefile b/GNUmakefile
index ecf8a60..12eca18 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -27,12 +27,18 @@ path = $(subst :, ,$(PATH))
 diet_path = $(foreach dir,$(path),$(wildcard $(dir)/diet))
 ifeq ($(strip $(diet_path)),)
 ifneq ($(wildcard /opt/diet/bin/diet),)
-DIET=/opt/diet/bin/diet -Os
+DIET=/opt/diet/bin/diet
 else
 DIET=
 endif
 else
-DIET:=$(strip $(diet_path)) -Os
+DIET:=$(strip $(diet_path))
+endif
+
+ifneq ($(DIET),)
+ifneq ($(DEBUG),1)
+DIET+=-Os
+endif
 endif
 # to build without diet libc support, use $ make DIET=
 # see http://www.fefe.de/dietlibc/ for details about the diet libc
diff --git a/io/io_waituntil.c b/io/io_waituntil.c
index 36bfbcb..929cc3e 100644
--- a/io/io_waituntil.c
+++ b/io/io_waituntil.c
@@ -5,9 +5,13 @@ void io_waituntil(tai6464 t) {
   uint64 x,y;
   tai6464 now,diff;
   taia_now(&now);
-  taia_sub(&diff,&t,&now);
-  if (!umult64(diff.sec.x,1000,&x) || (y=x+diff.nano/10000000)<x)
-    y=-1;	/* overflow; wait indefinitely */
-  if (!y && diff.nano) y=1;
+  if (taia_less(&t,&now))
+    y=0;
+  else {
+    taia_sub(&diff,&t,&now);
+    if (!umult64(diff.sec.x,1000,&x) || (y=x+diff.nano/1000000)<x)
+      y=-1;	/* overflow; wait indefinitely */
+    if (!y && diff.nano) y=1;
+  }
   io_waituntil2(y);
 }
diff --git a/io_internal.h b/io_internal.h
index ec38116..cdf7853 100644
--- a/io_internal.h
+++ b/io_internal.h
@@ -15,13 +15,13 @@ extern HANDLE io_comport;
 #endif
 
 typedef struct {
+  tai6464 timeout;
   unsigned int wantread:1;
   unsigned int wantwrite:1;
   unsigned int canread:1;
   unsigned int canwrite:1;
   unsigned int nonblock:1;
   unsigned int inuse:1;
-  tai6464 timeout;
   long next_read;
   long next_write;
   void* cookie;