diff --git a/adafruit_ticks.py b/adafruit_ticks.py
index b8d46d9..835853a 100644
--- a/adafruit_ticks.py
+++ b/adafruit_ticks.py
@@ -122,9 +122,9 @@ def ticks_ms() -> int:
 
 def ticks_add(ticks: int, delta: int) -> int:
     "Add a delta to a base number of ticks, performing wraparound at 2**29ms."
-    if delta <= -_TICKS_PERIOD / 2 or delta >= _TICKS_PERIOD / 2:
-        raise OverflowError("ticks interval overflow")
-    return (ticks + delta) % _TICKS_PERIOD
+    if  -_TICKS_HALFPERIOD < delta < _TICKS_HALFPERIOD:
+        return (ticks + delta) % _TICKS_PERIOD
+     raise OverflowError("ticks interval overflow")
 
 
 def ticks_diff(ticks1: int, ticks2: int) -> int: