diff --git a/Source/serial.cpp b/Source/serial.cpp
index 0dfd5fb..9bec5d8 100644
--- a/Source/serial.cpp
+++ b/Source/serial.cpp
@@ -7,6 +7,7 @@
 
 #include <cstdint>
 #include <cstdio>
+#include <errno.h>
 #include <sys/stat.h>
 #include <CLI.h>
 #include <stm32g0xx_ll_gpio.h>
@@ -14,6 +15,19 @@
 
 static char new_char = '\0';
 
+extern "C" int _getpid(void)
+{
+  return 1;
+}
+
+extern "C" int _kill(int pid, int sig)
+{
+  (void)pid;
+  (void)sig;
+  errno = EINVAL;
+  return -1;
+}
+
 extern "C" int _write(int file, char *ptr, int len)
 {
   (void)file;