diff --git a/assets/layers/charging_station/charging_station.json b/assets/layers/charging_station/charging_station.json
index d65d13e90b..354d98d270 100644
--- a/assets/layers/charging_station/charging_station.json
+++ b/assets/layers/charging_station/charging_station.json
@@ -2403,7 +2403,8 @@
         "de": "Wie lange darf man hier maximal parken?"
       },
       "freeform": {
-        "key": "maxstay"
+        "key": "maxstay",
+        "type": "pfloat"
       },
       "render": {
         "en": "One can stay at most <b>{canonical(maxstay)}</b>",
@@ -3329,4 +3330,4 @@
     },
     "neededChangesets": 10
   }
-}
\ No newline at end of file
+}
diff --git a/assets/layers/charging_station/charging_station.proto.json b/assets/layers/charging_station/charging_station.proto.json
index 4bbdde3f31..12cbcadf3a 100644
--- a/assets/layers/charging_station/charging_station.proto.json
+++ b/assets/layers/charging_station/charging_station.proto.json
@@ -564,7 +564,8 @@
         "nl": "Hoelang mag een voertuig hier blijven staan?"
       },
       "freeform": {
-        "key": "maxstay"
+        "key": "maxstay",
+        "type": "pfloat"
       },
       "render": {
         "en": "One can stay at most <b>{canonical(maxstay)}</b>",
@@ -1049,4 +1050,4 @@
     },
     "neededChangesets": 10
   }
-}
\ No newline at end of file
+}
diff --git a/assets/layers/entrance/entrance.json b/assets/layers/entrance/entrance.json
index 91bf1d8bc0..b26e76932f 100644
--- a/assets/layers/entrance/entrance.json
+++ b/assets/layers/entrance/entrance.json
@@ -515,7 +515,8 @@
         "cs": "Jaká je šířka těchto dveří/vchodu?"
       },
       "freeform": {
-        "key": "width"
+        "key": "width",
+        "type": "pfloat"
       }
     },
     {
diff --git a/src/Models/Unit.ts b/src/Models/Unit.ts
index 00ac6806d0..f1666b57e4 100644
--- a/src/Models/Unit.ts
+++ b/src/Models/Unit.ts
@@ -27,6 +27,10 @@ export class Unit {
     ) {
         this.quantity = quantity
         this._validator = validator
+        if(!inverted && ["string","text","key","icon","translation","fediverse","id"].indexOf(validator.name) >= 0){
+            console.trace("Unit error")
+            throw "Invalid unit configuration. The validator is of a forbidden type: "+validator.name+"; set a (number) type to your freeform key or set inverted. Hint: this unit is applied onto keys: "+appliesToKeys.join("; ")
+        }
         this.inverted = inverted
         this.appliesToKeys = new Set(appliesToKeys)
         this.denominations = applicableDenominations