diff --git a/KaitaiStruct.cs b/KaitaiStruct.cs
index 3e57143..42bcd0e 100644
--- a/KaitaiStruct.cs
+++ b/KaitaiStruct.cs
@@ -155,4 +155,14 @@ namespace Kaitai
 
         protected Object actual;
     }
+
+    public class ValidationExprError : ValidationFailedError {
+        public ValidationExprError(Object actual, KaitaiStream io, string srcPath)
+            : base("not matching the expression, got " + actual, io, srcPath)
+        {
+            this.actual = actual;
+        }
+
+        protected Object actual;
+    }
 }