diff --git a/include/exec_shell.h b/include/exec_shell.h
index a2aa757de..04aa089cc 100644
--- a/include/exec_shell.h
+++ b/include/exec_shell.h
@@ -1 +1,6 @@
-extern void __attribute__((__noreturn__)) exec_shell(void);
+#ifndef UTIL_LINUX_EXEC_SHELL_H
+#define UTIL_LINUX_EXEC_SHELL_H
+
+extern void exec_shell(void) __attribute__((__noreturn__));
+
+#endif /* UTIL_LINUX_EXEC_SHELL_H */
diff --git a/lib/exec_shell.c b/lib/exec_shell.c
index a7374bd33..b2f178add 100644
--- a/lib/exec_shell.c
+++ b/lib/exec_shell.c
@@ -30,7 +30,7 @@
 
 #define DEFAULT_SHELL "/bin/sh"
 
-void exec_shell(void)
+void __attribute__((__noreturn__)) exec_shell(void)
 {
 	const char *shell = getenv("SHELL");
 	char *shellc = xstrdup(shell);