diff --git a/bundles/org.openhab.transform.scale/conf/transform/scale/humidex.scale b/bundles/org.openhab.transform.scale/conf/transform/scale/humidex.scale
index 0ed152d56f713..eaa333e18b3bc 100644
--- a/bundles/org.openhab.transform.scale/conf/transform/scale/humidex.scale
+++ b/bundles/org.openhab.transform.scale/conf/transform/scale/humidex.scale
@@ -4,3 +4,4 @@
 [38..45]=avoid exertion
 [45..54]=dangerous
 [54..100]=heat stroke imminent
+NaN=unknown
diff --git a/bundles/org.openhab.transform.scale/src/main/java/org/openhab/transform/scale/internal/ScaleTransformationService.java b/bundles/org.openhab.transform.scale/src/main/java/org/openhab/transform/scale/internal/ScaleTransformationService.java
index 5e3a5b16095b8..8538657348ea2 100644
--- a/bundles/org.openhab.transform.scale/src/main/java/org/openhab/transform/scale/internal/ScaleTransformationService.java
+++ b/bundles/org.openhab.transform.scale/src/main/java/org/openhab/transform/scale/internal/ScaleTransformationService.java
@@ -129,7 +129,7 @@ private String formatResult(Map<Range, String> data, String source, final BigDec
 
     private String getScaleResult(Map<Range, String> data, String source, final BigDecimal value)
             throws TransformationException {
-        return data.entrySet().stream().filter(entry -> entry.getKey().contains(value)).findFirst()
+        return data.entrySet().stream().filter(entry -> entry.getKey() != null && entry.getKey().contains(value)).findFirst()
                 .map(Map.Entry::getValue)
                 .orElseThrow(() -> new TransformationException("No matching range for '" + source + "'"));
     }
diff --git a/bundles/org.openhab.transform.scale/src/test/java/org/openhab/transform/scale/internal/ScaleTransformServiceTest.java b/bundles/org.openhab.transform.scale/src/test/java/org/openhab/transform/scale/internal/ScaleTransformServiceTest.java
index a32a786417b67..17836e536badb 100644
--- a/bundles/org.openhab.transform.scale/src/test/java/org/openhab/transform/scale/internal/ScaleTransformServiceTest.java
+++ b/bundles/org.openhab.transform.scale/src/test/java/org/openhab/transform/scale/internal/ScaleTransformServiceTest.java
@@ -146,4 +146,12 @@ public void testTransformAndFormat() throws TransformationException {
         String transformedResponse = processor.transform(existingscale, source);
         Assert.assertEquals("Correcte (992) !", transformedResponse);
     }
+
+    @Test
+    public void testValueExceedsRange() throws TransformationException {
+        String existingscale = "scale/humidex.scale";
+        String source = "200";
+        String transformedResponse = processor.transform(existingscale, source);
+        Assert.assertEquals("", transformedResponse);
+    }
 }