diff --git a/modules/io/src/io_exception.hh b/modules/io/src/io_exception.hh
index beca6ec2d9cf523222d6ed313953fb821240a62f..483f98bca513a200aa6be6034c0229f85225993a 100644
--- a/modules/io/src/io_exception.hh
+++ b/modules/io/src/io_exception.hh
@@ -32,6 +32,12 @@ public:
     Error(m) {}
 };
 
+class IOUnknownFormatException: public Error {
+public:
+  IOUnknownFormatException(const String& m):
+    Error(m) {}
+};
+
 }} // ns
 
 #endif