diff --git a/src/main/org/apache/tools/ant/types/FilterSet.java b/src/main/org/apache/tools/ant/types/FilterSet.java
index 7235ea869..5429ba71e 100644
--- a/src/main/org/apache/tools/ant/types/FilterSet.java
+++ b/src/main/org/apache/tools/ant/types/FilterSet.java
@@ -326,6 +326,7 @@ public class FilterSet extends DataType implements Cloneable {
            throw new BuildException("Must specify a file not a directory in "
             + "the filtersfile attribute:" + filtersFile);
         }
+        filterHash = null;
     }
 
     /**