diff --git a/targets/demo/retarget.c b/targets/demo/retarget.c
index 7c53ba1..9ab40eb 100644
--- a/targets/demo/retarget.c
+++ b/targets/demo/retarget.c
@@ -19,6 +19,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#if !defined(__ARMCC_VERSION)
+#include <sys/stat.h>
+#endif
 #include <time.h>
 
 #include "uart_stdout.h"
@@ -222,6 +225,40 @@
     while (1) {}
 }
 
+#if !defined(__ARMCC_VERSION)
+int RETARGET(_fstat)(FILEHANDLE fh, struct stat *st) {
+    (void)fh;
+    (void)st;
+
+    return -1;
+}
+
+int RETARGET(_getpid)(void) {
+    return -1;
+}
+
+int RETARGET(_isatty)(FILEHANDLE fh) {
+    (void)fh;
+
+    return 0;
+}
+
+int RETARGET(_kill)(int pid, int sig) {
+    (void)pid;
+    (void)sig;
+
+    return -1;
+}
+
+int RETARGET(_lseek)(FILEHANDLE fh, int ptr, int dir) {
+    (void)fh;
+    (void)ptr;
+    (void)dir;
+
+    return -1;
+}
+#endif
+
 int system(const char *cmd) {
     (void)cmd;