diff --git a/common/a-reatim.ads b/common/a-reatim.ads
index 66f7d49..54d410b 100644
--- a/common/a-reatim.ads
+++ b/common/a-reatim.ads
@@ -33,6 +33,8 @@
 --                                                                          --
 ------------------------------------------------------------------------------
 
+--  Modified from GCC 4.9.1, then GCC 7.1.0, for Cortex GNAT RTS.
+
 package Ada.Real_Time with
   SPARK_Mode,
   Abstract_State => (Clock_Time with Synchronous,
@@ -149,9 +151,13 @@ private
    --  Replaces Duration, which has a different representation on
    --  systems with 32-bit Duration.
 
-   type Time is new Time_Base;
+   FreeRTOS_Tick : constant := 0.001;
+   --  FreeRTOSConfig.h has set configTICK_RATE_HZ to 1000
+
+   type Time is new Time_Base range 0.0 .. (2 ** 32 - 1) * FreeRTOS_Tick;
+   --  and configUSE_16_BIT_TICKS to 0 (so we get 32-bit clock values).
 
-   Time_First : constant Time := 0.0;
+   Time_First : constant Time := Time'First;
 
    Time_Last  : constant Time := Time'Last;
 
diff --git a/common/a-retide.adb b/common/a-retide.adb
index f0f1473..ac751cf 100644
--- a/common/a-retide.adb
+++ b/common/a-retide.adb
@@ -6,7 +6,7 @@
 --                                                                          --
 --                                  B o d y                                 --
 --                                                                          --
---      Copyright (C) 1992-2010, 2016, Free Software Foundation, Inc.       --
+--    Copyright (C) 1992-2010, 2016-2017, Free Software Foundation, Inc.    --
 --                                                                          --
 -- GNARL is free software; you can  redistribute it  and/or modify it under --
 -- terms of the  GNU General Public License as published  by the Free Soft- --
@@ -29,6 +29,8 @@
 --                                                                          --
 ------------------------------------------------------------------------------
 
+--  Modified from GCC 4.9.1 for Cortex GNAT RTS.
+
 with Interfaces;
 
 package body Ada.Real_Time.Delays is
@@ -40,12 +42,14 @@ package body Ada.Real_Time.Delays is
         Convention => C,
         External_Name => "vTaskDelay";
       Timespan_To_Delay : constant Time_Span := T - Clock;
-      --  ??? need to round, see ARM
-      Ticks_To_Delay : constant Integer := Timespan_To_Delay / Tick;
    begin
-      if Ticks_To_Delay > 0 then
+      if Timespan_To_Delay > 0.0 then
+         --  Need to avoid problems with ambiguity; and the version in
+         --  Real_Time returns Integer, whereas we actually want
+         --  Unsigned_32.
          vTaskDelay
-           (Ticks_To_Delay => Interfaces.Unsigned_32 (Ticks_To_Delay));
+           (Interfaces.Unsigned_32
+              (Standard."/" (Timespan_To_Delay, Tick)));
       end if;
    end Delay_Until;
 
diff --git a/test-arduino-due/testbed.adb b/test-arduino-due/testbed.adb
index c01237e..bfafa19 100644
--- a/test-arduino-due/testbed.adb
+++ b/test-arduino-due/testbed.adb
@@ -111,11 +111,5 @@ begin
    --  Check streams
    Streams.Check (42);
 
-   declare
-      use type Ada.Real_Time.Time;
-   begin
-      loop
-         delay until Ada.Real_Time.Clock + Ada.Real_Time.Seconds (10);
-      end loop;
-   end;
+   delay until Ada.Real_Time.Time_Last;
 end Testbed;
diff --git a/test-stm32f4/testbed.adb b/test-stm32f4/testbed.adb
index 027049c..f01d7d1 100644
--- a/test-stm32f4/testbed.adb
+++ b/test-stm32f4/testbed.adb
@@ -108,11 +108,5 @@ begin
    --  Check streams
    Streams.Check (42);
 
-   declare
-      use type Ada.Real_Time.Time;
-   begin
-      loop
-         delay until Ada.Real_Time.Clock + Ada.Real_Time.Seconds (10);
-      end loop;
-   end;
+   delay until Ada.Real_Time.Time_Last;
 end Testbed;
diff --git a/test-stm32f429i/testbed.adb b/test-stm32f429i/testbed.adb
index 027049c..f01d7d1 100644
--- a/test-stm32f429i/testbed.adb
+++ b/test-stm32f429i/testbed.adb
@@ -108,11 +108,5 @@ begin
    --  Check streams
    Streams.Check (42);
 
-   declare
-      use type Ada.Real_Time.Time;
-   begin
-      loop
-         delay until Ada.Real_Time.Clock + Ada.Real_Time.Seconds (10);
-      end loop;
-   end;
+   delay until Ada.Real_Time.Time_Last;
 end Testbed;