diff --git a/include/sway/config.h b/include/sway/config.h
index 7e67ba21..5a303d9f 100644
--- a/include/sway/config.h
+++ b/include/sway/config.h
@@ -688,8 +688,6 @@ const char *sway_output_scale_filter_to_string(enum scale_filter_mode scale_filt
 
 struct output_config *new_output_config(const char *name);
 
-void merge_output_config(struct output_config *dst, struct output_config *src);
-
 bool apply_output_configs(struct matched_output_config *configs,
 		size_t configs_len, bool test_only);
 
diff --git a/sway/config/output.c b/sway/config/output.c
index a7c2f9b8..72cbf261 100644
--- a/sway/config/output.c
+++ b/sway/config/output.c
@@ -79,7 +79,7 @@ struct output_config *new_output_config(const char *name) {
 	return oc;
 }
 
-void merge_output_config(struct output_config *dst, struct output_config *src) {
+static void merge_output_config(struct output_config *dst, struct output_config *src) {
 	if (src->enabled != -1) {
 		dst->enabled = src->enabled;
 	}