Index: tests/natools-time_io-tests.adb
==================================================================
--- tests/natools-time_io-tests.adb
+++ tests/natools-time_io-tests.adb
@@ -229,16 +229,29 @@
    procedure Read_From_RFC_3339 (Report : in out NT.Reporter'Class) is
       Test : NT.Test := Report.Item ("RFC-3339 -> Ada.Calendar.Time");
       Now : constant Extended_Time
         := (Ada.Calendar.Clock, Ada.Calendar.Time_Zones.UTC_Time_Offset);
 
-      function Value (Img : String) return Extended_Time;
+      function Value
+        (Img : String;
+         Expected_Leap : Boolean := False)
+        return Extended_Time;
 
-      function Value (Img : String) return Extended_Time is
+      function Value
+        (Img : String;
+         Expected_Leap : Boolean := False)
+        return Extended_Time
+      is
          Result : Extended_Time;
+         Leap : Boolean;
       begin
-         RFC_3339.Value (Img, Result.Time, Result.Offset);
+         RFC_3339.Value (Img, Result.Time, Result.Offset, Leap);
+         if Leap /= Expected_Leap then
+            Test.Fail ("Unexpected leap second flag at "
+              & Boolean'Image (Leap)
+              & " for """ & Img & '"');
+         end if;
          return Result;
       end Value;
    begin
       Check (Test,
          (Ada.Calendar.Formatting.Time_Of
@@ -262,10 +275,22 @@
          Check (Test,
             (Ada.Calendar.Formatting.Time_Of
               (1990, 12, 31, 15, 59, 59, 0.0, True, -8 * 60), -8 * 60),
             Value ("1990-12-31T15:59:60-08:00"),
             "[4] Leap second with time offset:");
+      else
+         Check (Test,
+            (Ada.Calendar.Formatting.Time_Of
+              (1990, 12, 31, 23, 59, 59, 0.0, False, 0), 0),
+            Value ("1990-12-31T23:59:60Z", True),
+            "[3] UTC leap second:");
+
+         Check (Test,
+            (Ada.Calendar.Formatting.Time_Of
+              (1990, 12, 31, 15, 59, 59, 0.0, False, -8 * 60), -8 * 60),
+            Value ("1990-12-31T15:59:60-08:00", True),
+            "[4] Leap second with time offset:");
       end if;
 
       Check (Test,
          (Ada.Calendar.Formatting.Time_Of
            (1937, 01, 01, 12, 0, 27, 0.87, False, 20), 20),
@@ -315,10 +340,26 @@
                  (1990, 12, 31, 15, 59, 59, 0.0, True, -8 * 60),
                -8 * 60, 0),
             "[4] Leap second with time offset:");
       end if;
 
+      Check (Test,
+         "1990-12-31T23:59:60Z",
+         RFC_3339.Image
+           (Ada.Calendar.Formatting.Time_Of
+              (1990, 12, 31, 23, 59, 59, 0.0, False, 0),
+            0, 0, True),
+         "[3b] UTC leap second with workaround:");
+
+      Check (Test,
+         "1990-12-31T15:59:60-08:00",
+         RFC_3339.Image
+           (Ada.Calendar.Formatting.Time_Of
+              (1990, 12, 31, 15, 59, 59, 0.0, False, -8 * 60),
+            -8 * 60, 0, True),
+         "[4b] Leap second with time offset and workaround:");
+
       Check (Test,
          "1937-01-01T12:00:27.87+00:20",
          RFC_3339.Image
            (Ada.Calendar.Formatting.Time_Of
               (1937, 01, 01, 12, 0, 27, 0.87, False, 20),