diff --git a/src/lib-sieve/plugins/vnd.dovecot/environment/Makefile.am b/src/lib-sieve/plugins/vnd.dovecot/environment/Makefile.am
index 5d4e438835c9d834538cd3913ee99c33960a45de..96618fffec27709a9d3339c72158ca8683804e9c 100644
--- a/src/lib-sieve/plugins/vnd.dovecot/environment/Makefile.am
+++ b/src/lib-sieve/plugins/vnd.dovecot/environment/Makefile.am
@@ -11,6 +11,6 @@ libsieve_ext_vnd_environment_la_SOURCES = \
 	ext-vnd-environment-items.c \
 	ext-vnd-environment-variables.c
 
-noinst_HEADERS =
+noinst_HEADERS = \
 	ext-vnd-environment-common.h