diff --git a/ports/zephyr/mstimer-init.c b/ports/zephyr/mstimer-init.c
index 460b4be5..bbbbd4b8 100644
--- a/ports/zephyr/mstimer-init.c
+++ b/ports/zephyr/mstimer-init.c
@@ -32,7 +32,7 @@
 */
 unsigned long mstimer_now(void)
 {
-    return (unsigned long) k_uptime_get();
+    return (unsigned long) k_uptime_get_32();
 }
 
 /**