diff --git a/libweston/backend-drm/modes.c b/libweston/backend-drm/modes.c
index 901372bb..37a10559 100644
--- a/libweston/backend-drm/modes.c
+++ b/libweston/backend-drm/modes.c
@@ -601,7 +601,7 @@ update_head_from_connector(struct drm_head *head)
 
 	weston_head_set_monitor_strings(&head->base, dhi.make ?: "unknown",
 					dhi.model ?: "unknown",
-					dhi.serial_number ?: "unknown");
+					dhi.serial_number);
 
 	prune_eotf_modes_by_kms_support(head, &dhi.eotf_mask);
 	weston_head_set_supported_eotf_mask(&head->base, dhi.eotf_mask);
diff --git a/pipewire/pipewire-plugin.c b/pipewire/pipewire-plugin.c
index cb07521a..3ab279b3 100644
--- a/pipewire/pipewire-plugin.c
+++ b/pipewire/pipewire-plugin.c
@@ -524,7 +524,6 @@ pipewire_output_create(struct weston_compositor *c, char *name)
 	const struct weston_drm_virtual_output_api *api;
 	const char *make = "Weston";
 	const char *model = "Virtual Display";
-	const char *serial_number = "unknown";
 	const char *connector_name = "pipewire";
 	char *remoting_name;
 
@@ -566,7 +565,7 @@ pipewire_output_create(struct weston_compositor *c, char *name)
 	str_printf(&remoting_name, "%s-%s", connector_name, name);
 	weston_head_init(head, remoting_name);
 	weston_head_set_subpixel(head, WL_OUTPUT_SUBPIXEL_NONE);
-	weston_head_set_monitor_strings(head, make, model, serial_number);
+	weston_head_set_monitor_strings(head, make, model, NULL);
 	head->compositor = c;
 	output->head = head;
 
diff --git a/remoting/remoting-plugin.c b/remoting/remoting-plugin.c
index 4d4dea7e..b517ee70 100644
--- a/remoting/remoting-plugin.c
+++ b/remoting/remoting-plugin.c
@@ -752,7 +752,6 @@ remoting_output_create(struct weston_compositor *c, char *name)
 	const struct weston_drm_virtual_output_api *api;
 	const char *make = "Renesas";
 	const char *model = "Virtual Display";
-	const char *serial_number = "unknown";
 	const char *connector_name = "remoting";
 	char *remoting_name;
 
@@ -790,7 +789,7 @@ remoting_output_create(struct weston_compositor *c, char *name)
 	str_printf(&remoting_name, "%s-%s", connector_name, name);
 	weston_head_init(head, remoting_name);
 	weston_head_set_subpixel(head, WL_OUTPUT_SUBPIXEL_NONE);
-	weston_head_set_monitor_strings(head, make, model, serial_number);
+	weston_head_set_monitor_strings(head, make, model, NULL);
 	head->compositor = c;
 
 	weston_output_attach_head(output->output, head);