diff --git a/.hgignore b/.hgignore
index 2375ef177..28623a76b 100644
--- a/.hgignore
+++ b/.hgignore
@@ -13,7 +13,6 @@ autom4te.cache
 config.log
 config.status
 include/setup.h
-include/serno.h
 libratbox/include/libratbox_config.h
 libratbox/include/librb-config.h
 libratbox/include/stamp-h1
diff --git a/libratbox/include/serno.h b/libratbox/include/serno.h
new file mode 100644
index 000000000..01d83fe98
--- /dev/null
+++ b/libratbox/include/serno.h
@@ -0,0 +1 @@
+#define SERNO "20081221-ce6b9f338462"