diff --git a/attach.c b/attach.c
index 22d7a93..63e21c6 100644
--- a/attach.c
+++ b/attach.c
@@ -93,7 +93,7 @@ int *get_child_tty_fds(struct ptrace_child *child, int statfd, int *count) {
     if ((child->error = parse_proc_stat(statfd, &child_status)))
         return NULL;
 
-    debug("Resolved child tty: %u", child_status.ctty);
+    debug("Resolved child tty: %x", (unsigned)child_status.ctty);
 
     if (stat("/dev/tty", &tty_st) < 0) {
         child->error = errno;
@@ -169,7 +169,7 @@ int do_setsid(struct ptrace_child *child) {
     if (err < 0)
         return err;
 
-    debug("Forked a child: %d", child->forked_pid);
+    debug("Forked a child: %ld", child->forked_pid);
 
     err = ptrace_finish_attach(&dummy, child->forked_pid);
     if (err < 0)
diff --git a/reptyr.h b/reptyr.h
index f2fc29e..0fbd48b 100644
--- a/reptyr.h
+++ b/reptyr.h
@@ -23,6 +23,7 @@
 #define REPTYR_VERSION "0.2dev"
 
 int attach_child(pid_t pid, const char *pty, int force_stdio);
-void die(const char *msg, ...);
-void debug(const char *msg, ...);
-void error(const char *msg, ...);
+#define __printf __attribute__((format(printf, 1, 2)))
+void __printf die(const char *msg, ...);
+void __printf debug(const char *msg, ...);
+void __printf error(const char *msg, ...);