diff --git a/btpd/main.c b/btpd/main.c
index 247e0f7..c43c223 100644
--- a/btpd/main.c
+++ b/btpd/main.c
@@ -9,7 +9,7 @@ static void
 writepid(int pidfd)
 {
     FILE *fp = fdopen(dup(pidfd), "w");
-    fprintf(fp, "%d", getpid());
+    fprintf(fp, "%ld", (long)getpid());
     fclose(fp);
 }