diff --git a/include/json/value.h b/include/json/value.h
index 68fc163..8e996ae 100644
--- a/include/json/value.h
+++ b/include/json/value.h
@@ -37,21 +37,36 @@ namespace Json {
  *
  * We use nothing but these internally. Of course, STL can throw others.
  */
-class JSON_API Exception;
+class JSON_API Exception : public std::exception {
+public:
+  Exception(std::string const& msg);
+  virtual ~Exception() throw();
+  virtual char const* what() const throw();
+protected:
+  std::string const msg_;
+};
+
 /** Exceptions which the user cannot easily avoid.
  *
  * E.g. out-of-memory (when we use malloc), stack-overflow, malicious input
  * 
  * \remark derived from Json::Exception
  */
-class JSON_API RuntimeError;
+class JSON_API RuntimeError : public Exception {
+public:
+  RuntimeError(std::string const& msg);
+};
+
 /** Exceptions thrown by JSON_ASSERT/JSON_FAIL macros.
  *
  * These are precondition-violations (user bugs) and internal errors (our bugs).
  * 
  * \remark derived from Json::Exception
  */
-class JSON_API LogicError;
+class JSON_API LogicError : public Exception {
+public:
+  LogicError(std::string const& msg);
+};
 
 /// used internally
 void throwRuntimeError(std::string const& msg);
diff --git a/src/lib_json/json_value.cpp b/src/lib_json/json_value.cpp
index 231089f..9a16491 100644
--- a/src/lib_json/json_value.cpp
+++ b/src/lib_json/json_value.cpp
@@ -152,23 +152,6 @@ static inline void releaseStringValue(char* value) { free(value); }
 
 namespace Json {
 
-class JSON_API Exception : public std::exception {
-public:
-  Exception(std::string const& msg);
-  virtual ~Exception() throw();
-  virtual char const* what() const throw();
-protected:
-  std::string const msg_;
-};
-class JSON_API RuntimeError : public Exception {
-public:
-  RuntimeError(std::string const& msg);
-};
-class JSON_API LogicError : public Exception {
-public:
-  LogicError(std::string const& msg);
-};
-
 Exception::Exception(std::string const& msg)
   : msg_(msg)
 {}