diff --git a/src/runtime/runtime_esp32c3.go b/src/runtime/runtime_esp32c3.go
index 013c93924..f85f7dec7 100644
--- a/src/runtime/runtime_esp32c3.go
+++ b/src/runtime/runtime_esp32c3.go
@@ -54,10 +54,6 @@ func main() {
 	// Configure interrupt handler
 	interruptInit()
 
-	// Initialize UART.
-	machine.USBCDC.Configure(machine.UARTConfig{})
-	machine.InitSerial()
-
 	// Initialize main system timer used for time.Now.
 	initTimer()
 
@@ -68,6 +64,11 @@ func main() {
 	exit(0)
 }
 
+func init() {
+	// Initialize UART.
+	machine.InitSerial()
+}
+
 func abort() {
 	// lock up forever
 	for {
diff --git a/src/runtime/runtime_esp32s3.go b/src/runtime/runtime_esp32s3.go
index ab0d85d73..b469ddf9e 100644
--- a/src/runtime/runtime_esp32s3.go
+++ b/src/runtime/runtime_esp32s3.go
@@ -72,9 +72,6 @@ func main() {
 		clearbss()
 	}
 
-	// Initialize UART.
-	machine.InitSerial()
-
 	// Initialize main system timer used for time.Now.
 	initTimer()
 
@@ -85,6 +82,11 @@ func main() {
 	exit(0)
 }
 
+func init() {
+	// Initialize UART.
+	machine.InitSerial()
+}
+
 func abort() {
 	// lock up forever
 	print("abort called\n")