diff --git a/src/helma/util/ResourceProperties.java b/src/helma/util/ResourceProperties.java
index 96f34bc1..3a375f24 100644
--- a/src/helma/util/ResourceProperties.java
+++ b/src/helma/util/ResourceProperties.java
@@ -482,8 +482,8 @@ public class ResourceProperties extends Properties {
      * @return the old value, if an old value got replaced
      */
     public Object put(Object key, Object value) {
-        if (value != null) {
-            value = value.toString().trim();
+        if (value instanceof String) {
+            value = ((String) value).trim();
         }
         String strkey = key.toString();
         if (ignoreCase) {