diff --git a/boot/boot_serial/src/boot_serial.c b/boot/boot_serial/src/boot_serial.c
index 88c0029c0..c1d2a1e57 100644
--- a/boot/boot_serial/src/boot_serial.c
+++ b/boot/boot_serial/src/boot_serial.c
@@ -613,6 +613,7 @@ boot_serial_start(const struct boot_uart_funcs *f)
 
     off = 0;
     while (1) {
+        MCUBOOT_CPU_IDLE();
         rc = f->read(in_buf + off, sizeof(in_buf) - off, &full_line);
         if (rc <= 0 && !full_line) {
             continue;