diff --git a/railway-electrification.json b/railway-electrification.json
index f54ba20c..f116ad1b 100644
--- a/railway-electrification.json
+++ b/railway-electrification.json
@@ -15,14 +15,18 @@
     "feature": {
         "pre": [
             "{% if tags.electrified and tags.electrified != 'no' %}",
-            "  {% if tags.voltage < 1000 %}",
+            "  {% if not tags.voltage is defined %}",
+            "    {% set color = '#7f7f7f' %}",
+            "  {% elseif not tags.voltage|matches('^[0-9]+$') %}",
+            "    {% set color = '#ff0000' %}",
+            "  {% elseif tags.voltage < 1000 %}",
             "    {% set color = colorInterpolate([ '#00ff00', 'blue' ], tags.voltage / 1000) %}",
             "  {% else %}",
-            "    {% set color = colorInterpolate([ 'blue', 'red' ], (tags.voltage - 1000) / 24000) %}",
+            "    {% set color = colorInterpolate([ 'blue', '#af0000' ], (tags.voltage - 1000) / 24000) %}",
             "  {% endif %}",
             "{% else %}",
-            "  {% set color='black' %}",
-            "{%endif %}",
+            "  {% set color = 'black' %}",
+            "{% endif %}",
             "",
             "{% if tags.service == 'yard' or tags.service == 'siding' or tags.service == 'spur' or tags.service == 'crossover' %}",
             "    {% set width=2 %}",
@@ -67,7 +71,7 @@
             "opacity": "1",
             "fill": null,
             "dashArray": [
-                "{% if not tags.electrified or tags.electrified == 'no' %}",
+                "{% if not tags.electrified is defined  %}",
                 "{% elseif tags.frequency == 0 %}",
                 "{% else %}",
                 "5,2",
@@ -97,7 +101,7 @@
         "{% endfor %}",
         "",
         "{% for i in range(3000, 25000, 2000) %}",
-        "  {% set color = colorInterpolate([ 'blue', 'red' ], (i - 1000) / 24000) %}",
+        "  {% set color = colorInterpolate([ 'blue', '#af0000' ], (i - 1000) / 24000) %}",
         "  <tr>",
         "    <td>{{ markerLine({ 'width': 3, 'color': color })|raw }}</td>",
         "    <td>{{ i }}V</td>",
@@ -113,6 +117,16 @@
         "    <td>{{ markerLine({ 'styles': [ 'casing', 'default' ], 'style:casing': { 'width': 3, 'color': 'white' }, 'style': { 'width': '3', 'dashArray': '5,2', 'lineCap': 'butt', 'color': color } })|raw }}</td>",
         "    <td>{{ trans('alternating current') }}</td>",
         "  </tr>",
+        "",
+        "  <tr>",
+        "    <td>{{ markerLine({ 'width': 3, 'color': '#7f7f7f' })|raw }}</td>",
+        "    <td>{{ trans('unknown') }}</td>",
+        "  </tr>",
+        "",
+        "  <tr>",
+        "    <td>{{ markerLine({ 'width': 3, 'color': '#ff0000' })|raw }}</td>",
+        "    <td>{{ trans('illegal value') }}</td>",
+        "  </tr>",
         "</table>"
     ]
 }