diff --git a/src/lib-sieve/plugins/environment/ext-environment-common.c b/src/lib-sieve/plugins/environment/ext-environment-common.c
index 9797169053b6f05badb5266fc734f2927deeef8b..22c766ee158c95b5aefa8750c514dd92f08f6e8c 100644
--- a/src/lib-sieve/plugins/environment/ext-environment-common.c
+++ b/src/lib-sieve/plugins/environment/ext-environment-common.c
@@ -98,7 +98,7 @@ const struct sieve_environment_item domain_env_item = {
  *   executing.
  */
 
-const char *envit_host_get_value(const struct sieve_script_env *senv)
+static const char *envit_host_get_value(const struct sieve_script_env *senv)
 {
 	return senv->hostname != NULL ? senv->hostname : "";
 }