diff --git a/uart.c b/uart.c
index 369ad15..83dbf6a 100644
--- a/uart.c
+++ b/uart.c
@@ -5,6 +5,9 @@
 #include <libopencm3/stm32/rcc.h>
 #include <libopencm3/stm32/usart.h>
 #include <stdio.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
 #include <unistd.h>
 
 int _write(int file, char *ptr, int len);
@@ -36,3 +39,39 @@ int _write(int file, char *ptr, int len) {
     errno = EIO;
     return -1;
 }
+
+int _close(int file);
+int _close(int file) {
+    (void)file;
+    return -1;
+}
+
+int _fstat(int file, struct stat *st);
+int _fstat(int file, struct stat *st) {
+    (void)file;
+    st->st_mode = S_IFCHR;
+    return 0;
+}
+
+int _isatty(int file);
+int _isatty(int file) {
+    (void)file;
+    return 1;
+}
+
+int _lseek(int file, int ptr, int dir);
+int _lseek(int file, int ptr, int dir) {
+    (void)file;
+    (void)ptr;
+    (void)dir;
+    return 0;
+}
+
+// Optional — stubbed read (e.g. for scanf), returns 0 bytes
+int _read(int file, char *ptr, int len);
+int _read(int file, char *ptr, int len) {
+    (void)file;
+    (void)ptr;
+    (void)len;
+    return 0;
+}