diff --git a/test/time.carp b/test/time.carp
index fb3b58f..4f8cfc3 100644
--- a/test/time.carp
+++ b/test/time.carp
@@ -682,6 +682,62 @@
                         (Maybe.Nothing))
         3600))
     "add 3600 seconds is one hour")
+  (assert-equal test
+    &@"2088-01-20 03:14:06"
+    &(stamp
+      &(Datetime.add-seconds
+        &(Datetime.init 2020
+                        1
+                        1
+                        (Maybe.Just 23)
+                        (Maybe.Just 59)
+                        (Maybe.Just 59)
+                        (Maybe.Nothing)
+                        (Maybe.Nothing))
+        2147483647))
+    "add Int.MAX seconds to a non-zero seconds field")
+  (assert-equal test
+    &@"1951-12-14 20:45:51"
+    &(stamp
+      &(Datetime.add-seconds
+        &(Datetime.init 2020
+                        1
+                        1
+                        (Maybe.Just 23)
+                        (Maybe.Just 59)
+                        (Maybe.Just 59)
+                        (Maybe.Nothing)
+                        (Maybe.Nothing))
+        -2147483648))
+    "add Int.MIN seconds to a non-zero seconds field")
+  (assert-equal test
+    &@"2063-05-18 03:33:19"
+    &(stamp
+      &(Datetime.add-seconds
+        &(Datetime.init 1999
+                        12
+                        31
+                        (Maybe.Just 23)
+                        (Maybe.Just 59)
+                        (Maybe.Just 59)
+                        (Maybe.Nothing)
+                        (Maybe.Nothing))
+        2000000000))
+    "add 2000000000 seconds")
+  (assert-equal test
+    &@"2056-09-09 01:46:39"
+    &(stamp
+      &(Datetime.add-seconds
+        &(Datetime.init 2024
+                        12
+                        31
+                        (Maybe.Just 23)
+                        (Maybe.Just 59)
+                        (Maybe.Just 59)
+                        (Maybe.Nothing)
+                        (Maybe.Nothing))
+        1000000000))
+    "add 1000000000 seconds")
 
   (assert-equal test
     &@"2024-03-15"
diff --git a/time.carp b/time.carp
index 11ded36..b8dc40c 100644
--- a/time.carp
+++ b/time.carp
@@ -295,25 +295,26 @@ If `n` is negative, it will be subtracted instead.")
                     (set-year! &nd @(year &nnd))
                     nd)))))))
       (let-do [nd @d
+               days (/ n DAY)
                s (Maybe.from @(seconds d) 0)
-               a (+ s n)]
+               a (+ s (Int.mod n DAY))]
         (set-seconds! &nd (Maybe.Just (Int.mod a 60)))
-        (if (< a 60)
+        (if (and (< a 60) (= days 0))
           nd
           (let-do [m (/ a 60)
                    dm (Maybe.from @(minutes d) 0)
                    ma (+ m dm)]
             (set-minutes! &nd (Maybe.Just (Int.mod ma 60)))
-            (if (< ma 60)
+            (if (and (< ma 60) (= days 0))
               nd
               (let-do [h (/ ma 60)
                        dh (Maybe.from @(hours d) 0)
                        ha (+ h dh)]
                 (set-hours! &nd (Maybe.Just (Int.mod ha 24)))
-                (if (< ha 24)
+                (if (and (< ha 24) (= days 0))
                   nd
                   (let-do [ord (to-ordinal d)
-                           nnd (from-ordinal (+ ord (/ ha 24)))]
+                           nnd (from-ordinal (+ ord (+ days (/ ha 24))))]
                     (set-day! &nd @(day &nnd))
                     (set-month! &nd @(month &nnd))
                     (set-year! &nd @(year &nnd))