diff --git a/KaitaiStruct.cs b/KaitaiStruct.cs
index aa60c98..0fe152f 100644
--- a/KaitaiStruct.cs
+++ b/KaitaiStruct.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Text;
 
 namespace Kaitai
 {
@@ -34,4 +35,70 @@ public interface CustomDecoder
         /// <param name="src">Source byte array.</param>
         byte[] Decode(byte[] src);
     }
+
+    /// <summary>
+    /// Common ancestor for all error originating from Kaitai Struct usage.
+    /// Stores KSY source path, pointing to an element supposedly guilty of
+    /// an error.
+    /// </summary>
+    public class KaitaiStructError : Exception {
+        public KaitaiStructError(string msg, string srcPath)
+            : base(srcPath + ": " + msg)
+        {
+            this.srcPath = srcPath;
+        }
+
+        protected string srcPath;
+    }
+
+    /// <summary>
+    /// Common ancestor for all validation failures. Stores pointer to
+    /// KaitaiStream IO object which was involved in an error.
+    /// </summary>
+    public class ValidationFailedError : KaitaiStructError {
+        public ValidationFailedError(string msg, KaitaiStream io, string srcPath)
+            : base("at pos " + io.Pos + ": validation failed: " + msg, srcPath)
+        {
+            this.io = io;
+        }
+
+        protected KaitaiStream io;
+
+        protected static string ByteArrayToHex(byte[] arr) {
+            StringBuilder sb = new StringBuilder("[");
+            for (int i = 0; i < arr.Length; i++)
+            {
+                if (i > 0)
+                {
+                    sb.Append(' ');
+                }
+                sb.Append(string.Format("{0:X2}", arr[i]));
+            }
+            sb.Append(']');
+            return sb.ToString();
+        }
+    }
+
+    /// <summary>
+    /// Signals validation failure: we required "actual" value to be equal to
+    /// "expected", but it turned out that it's not.
+    /// </summary>
+    public class ValidationNotEqualError : ValidationFailedError {
+        public ValidationNotEqualError(byte[] expected, byte[] actual, KaitaiStream io, string srcPath)
+            : base("not equal, expected " + ByteArrayToHex(expected) + ", but got " + ByteArrayToHex(actual), io, srcPath)
+        {
+            this.expected = expected;
+            this.actual = actual;
+        }
+
+        public ValidationNotEqualError(Object expected, Object actual, KaitaiStream io, string srcPath)
+            : base("not equal, expected " + expected + ", but got " + actual, io, srcPath)
+        {
+            this.expected = expected;
+            this.actual = actual;
+        }
+
+        protected Object expected;
+        protected Object actual;
+    }
 }