diff --git a/apps/client/src/components/dispatch/map/smart-motorway-signs/smart-motorway-sign-marker.tsx b/apps/client/src/components/dispatch/map/smart-motorway-signs/smart-motorway-sign-marker.tsx
index ababa497d..859e596f1 100644
--- a/apps/client/src/components/dispatch/map/smart-motorway-signs/smart-motorway-sign-marker.tsx
+++ b/apps/client/src/components/dispatch/map/smart-motorway-signs/smart-motorway-sign-marker.tsx
@@ -50,7 +50,7 @@ export function SmartMotorwaySignsMarker({ marker }: Props) {
 
   React.useEffect(() => {
     const speeds = marker.speeds ?? marker.defaultSpeeds;
-    if (speeds) {
+    if (Array.isArray(speeds)) {
       setMarkerConfiguration(speeds.map((speed) => String(speed)));
     }
   }, [marker.speeds, marker.defaultSpeeds]);