diff --git a/library/server/wsf/router/documentation/wsf_router_self_documentation_handler.e b/library/server/wsf/router/documentation/wsf_router_self_documentation_handler.e
index b0fbb6da..8ab6c2ab 100644
--- a/library/server/wsf/router/documentation/wsf_router_self_documentation_handler.e
+++ b/library/server/wsf/router/documentation/wsf_router_self_documentation_handler.e
@@ -26,14 +26,27 @@ create
 feature {NONE} -- Initialization
 
 	make (a_router: WSF_ROUTER)
+			-- Initialize `router'.
+		require
+			a_router_attached: a_router /= Void
 		do
 			router := a_router
+		ensure
+			router_aliased: router = a_router
+			not_hidden: not is_hidden
 		end
 
 	make_hidden (a_router: WSF_ROUTER)
+			-- Initialize `router'.
+			-- Do not display documentation for `a_router'.
+		require
+			a_router_attached: a_router /= Void
 		do
 			make (a_router)
 			is_hidden := True
+		ensure
+			router_aliased: router = a_router
+			hidden: is_hidden	
 		end
 
 	router: WSF_ROUTER
@@ -46,6 +59,7 @@ feature {NONE} -- Initialization
 feature -- Documentation
 
 	mapping_documentation (m: WSF_ROUTER_MAPPING; a_request_methods: detachable WSF_REQUEST_METHODS): WSF_ROUTER_MAPPING_DOCUMENTATION
+			-- <Precursor>
 		do
 			create Result.make (m)
 			Result.set_is_hidden (is_hidden)
@@ -76,4 +90,8 @@ feature -- Execution
 			res.send (m)
 		end
 
+invariant
+
+	router_attached: router /= Void
+
 end
diff --git a/library/server/wsf/router/documentation/wsf_self_documented_handler.e b/library/server/wsf/router/documentation/wsf_self_documented_handler.e
index 453ee958..ecc23695 100644
--- a/library/server/wsf/router/documentation/wsf_self_documented_handler.e
+++ b/library/server/wsf/router/documentation/wsf_self_documented_handler.e
@@ -12,7 +12,12 @@ feature -- Documentation
 	mapping_documentation (m: WSF_ROUTER_MAPPING; a_request_methods: detachable WSF_REQUEST_METHODS): WSF_ROUTER_MAPPING_DOCUMENTATION
 			-- Documentation associated with Current handler, in the context of the mapping `m' and methods `a_request_methods'.
 			--| `m' and `a_request_methods' are useful to produce specific documentation when the handler is used for multiple mapping.
+		require
+			m_attached: m /= Void
+			a_request_methods_attached: a_request_methods /= Void
 		deferred
+		ensure
+			mapping_documentation_attached: Result /= Void
 		end
 
 end
diff --git a/library/server/wsf/router/wsf_handler.e b/library/server/wsf/router/wsf_handler.e
index 1470a08d..3d15e03f 100644
--- a/library/server/wsf/router/wsf_handler.e
+++ b/library/server/wsf/router/wsf_handler.e
@@ -11,6 +11,8 @@ feature -- Status report
 
 	is_valid_context (req: WSF_REQUEST): BOOLEAN
 			-- Is `req' valid context for current handler?
+		require
+			req_attached: req /= Void
 		do
 			Result := True
 		end
@@ -19,6 +21,8 @@ feature {WSF_ROUTER} -- Mapping
 
 	on_mapped (a_mapping: WSF_ROUTER_MAPPING; a_rqst_methods: detachable WSF_REQUEST_METHODS)
 			-- Callback called when a router map a route to Current handler
+		require
+			a_mapping_attached: a_mapping /= Void
 		do
 		end