diff --git a/src/cards/ha-weather-card.js b/src/cards/ha-weather-card.js
index 093c41a771..d37790fe1c 100644
--- a/src/cards/ha-weather-card.js
+++ b/src/cards/ha-weather-card.js
@@ -203,7 +203,7 @@ class HaWeatherCard extends
   }
 
   getUnit(measure) {
-    const lengthUnit = this.hass.config.core.unit_system.length;
+    const lengthUnit = this.hass.config.core.unit_system.length || '';
     switch (measure) {
       case 'air_pressure':
         return lengthUnit === 'km' ? 'hPa' : 'inHg';
diff --git a/src/dialogs/more-info/controls/more-info-weather.js b/src/dialogs/more-info/controls/more-info-weather.js
index e783c53f45..2b53467d00 100644
--- a/src/dialogs/more-info/controls/more-info-weather.js
+++ b/src/dialogs/more-info/controls/more-info-weather.js
@@ -156,7 +156,7 @@ class MoreInfoWeather extends LocalizeMixin(PolymerElement) {
   }
 
   getUnit(measure) {
-    const lengthUnit = this.hass.config.core.unit_system.length;
+    const lengthUnit = this.hass.config.core.unit_system.length || '';
     switch (measure) {
       case 'air_pressure':
         return lengthUnit === 'km' ? 'hPa' : 'inHg';