diff --git a/sys/stdio_uart/Makefile b/sys/stdio_uart/Makefile
index 7f3b72f4a6..48422e909a 100644
--- a/sys/stdio_uart/Makefile
+++ b/sys/stdio_uart/Makefile
@@ -1,4 +1 @@
-ifeq (gnu, $(TOOLCHAIN))
-  CFLAGS += -Wno-cast-function-type
-endif
 include $(RIOTBASE)/Makefile.base
diff --git a/sys/stdio_uart/stdio_uart.c b/sys/stdio_uart/stdio_uart.c
index 07c12a34f3..19e0530f8b 100644
--- a/sys/stdio_uart/stdio_uart.c
+++ b/sys/stdio_uart/stdio_uart.c
@@ -30,11 +30,11 @@
 #include <errno.h>
 #include <string.h>
 
-#include "stdio_uart.h"
-
 #include "board.h"
-#include "periph/uart.h"
 #include "isrpipe.h"
+#include "kernel_defines.h"
+#include "periph/uart.h"
+#include "stdio_uart.h"
 
 #if MODULE_VFS
 #include "vfs.h"
@@ -43,23 +43,23 @@
 #define ENABLE_DEBUG 0
 #include "debug.h"
 
-#ifdef MODULE_STDIO_UART_RX
 static uint8_t _rx_buf_mem[STDIO_UART_RX_BUFSIZE];
 isrpipe_t stdio_uart_isrpipe = ISRPIPE_INIT(_rx_buf_mem);
-#endif
+
+static void _isrpipe_write_one_wrapper(void *arg, uint8_t value)
+{
+    isrpipe_write_one(arg, value);
+}
 
 void stdio_init(void)
 {
-    uart_rx_cb_t cb;
-    void *arg;
+    uart_rx_cb_t cb = NULL;
+    void *arg = NULL;
 
-#ifdef MODULE_STDIO_UART_RX
-    cb = (uart_rx_cb_t) isrpipe_write_one;
-    arg = &stdio_uart_isrpipe;
-#else
-    cb = NULL;
-    arg = NULL;
-#endif
+    if (IS_USED(MODULE_STDIO_UART_RX)) {
+        cb = _isrpipe_write_one_wrapper;
+        arg = &stdio_uart_isrpipe;
+    }
 
     uart_init(STDIO_UART_DEV, STDIO_UART_BAUDRATE, cb, arg);
 
@@ -77,13 +77,10 @@ int stdio_available(void)
 
 ssize_t stdio_read(void* buffer, size_t count)
 {
-#ifdef MODULE_STDIO_UART_RX
-    return (ssize_t)isrpipe_read(&stdio_uart_isrpipe, buffer, count);
-#else
-    (void)buffer;
-    (void)count;
+    if (IS_USED(MODULE_STDIO_UART_RX)) {
+        return (ssize_t)isrpipe_read(&stdio_uart_isrpipe, buffer, count);
+    }
     return -ENOTSUP;
-#endif
 }
 
 ssize_t stdio_write(const void *buffer, size_t len)