diff --git a/ports/zephyr/mphalport.h b/ports/zephyr/mphalport.h
index 594f6a1f69..8434a388b0 100644
--- a/ports/zephyr/mphalport.h
+++ b/ports/zephyr/mphalport.h
@@ -21,7 +21,7 @@ static inline void mp_hal_delay_us(mp_uint_t delay) {
 }
 
 static inline void mp_hal_delay_ms(mp_uint_t delay) {
-    k_sleep(delay);
+    k_msleep(delay);
 }
 
 #define mp_hal_delay_us_fast(us)   (mp_hal_delay_us(us))
diff --git a/ports/zephyr/uart_core.c b/ports/zephyr/uart_core.c
index fef9f00ab1..63ecc8289e 100644
--- a/ports/zephyr/uart_core.c
+++ b/ports/zephyr/uart_core.c
@@ -49,7 +49,7 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     while (len--) {
         char c = *str++;
         while (console_putchar(c) == -1) {
-            k_sleep(1);
+            k_msleep(1);
         }
     }
     #else