diff --git a/vendor/manifest b/vendor/manifest
index a271175c..8681132a 100644
--- a/vendor/manifest
+++ b/vendor/manifest
@@ -92,7 +92,7 @@
 		{
 			"importpath": "github.com/matrix-org/util",
 			"repository": "https://github.com/matrix-org/util",
-			"revision": "0bbc3896e02031e7e7338948b73ce891aa73ab2b",
+			"revision": "4de125c773716ad380f2f80cc6c04789ef4c906a",
 			"branch": "master"
 		},
 		{
diff --git a/vendor/src/github.com/matrix-org/util/error.go b/vendor/src/github.com/matrix-org/util/error.go
index 9d40c57b..530a581b 100644
--- a/vendor/src/github.com/matrix-org/util/error.go
+++ b/vendor/src/github.com/matrix-org/util/error.go
@@ -5,8 +5,14 @@ import "fmt"
 // HTTPError An HTTP Error response, which may wrap an underlying native Go Error.
 type HTTPError struct {
 	WrappedError error
-	Message      string
-	Code         int
+	// A human-readable message to return to the client in a JSON response. This
+	// is ignored if JSON is supplied.
+	Message string
+	// HTTP status code.
+	Code int
+	// JSON represents the JSON that should be serialized and sent to the client
+	// instead of the given Message.
+	JSON interface{}
 }
 
 func (e HTTPError) Error() string {
diff --git a/vendor/src/github.com/matrix-org/util/json.go b/vendor/src/github.com/matrix-org/util/json.go
index b310ac92..92604c54 100644
--- a/vendor/src/github.com/matrix-org/util/json.go
+++ b/vendor/src/github.com/matrix-org/util/json.go
@@ -68,7 +68,10 @@ func Protect(handler http.HandlerFunc) http.HandlerFunc {
 					"Request panicked!\n%s", debug.Stack(),
 				)
 				jsonErrorResponse(
-					w, req, &HTTPError{nil, "Internal Server Error", 500},
+					w, req, &HTTPError{
+						Message: "Internal Server Error",
+						Code:    500,
+					},
 				)
 			}
 		}()
@@ -112,7 +115,10 @@ func MakeJSONAPI(handler JSONRequestHandler) http.HandlerFunc {
 		if !ok {
 			r, err := json.Marshal(res)
 			if err != nil {
-				jsonErrorResponse(w, req, &HTTPError{nil, "Failed to serialise response as JSON", 500})
+				jsonErrorResponse(w, req, &HTTPError{
+					Message: "Failed to serialise response as JSON",
+					Code:    500,
+				})
 				return
 			}
 			resBytes = r
@@ -135,9 +141,23 @@ func jsonErrorResponse(w http.ResponseWriter, req *http.Request, httpErr *HTTPEr
 
 	w.WriteHeader(httpErr.Code) // Set response code
 
-	r, err := json.Marshal(&JSONError{
-		Message: httpErr.Message,
-	})
+	var err error
+	var r []byte
+	if httpErr.JSON != nil {
+		r, err = json.Marshal(httpErr.JSON)
+		if err != nil {
+			// failed to marshal the supplied interface. Whine and fallback to the HTTP message.
+			logger.WithError(err).Error("Failed to marshal HTTPError.JSON")
+		}
+	}
+
+	// failed to marshal or no custom JSON was supplied, send message JSON.
+	if err != nil || httpErr.JSON == nil {
+		r, err = json.Marshal(&JSONError{
+			Message: httpErr.Message,
+		})
+	}
+
 	if err != nil {
 		// We should never fail to marshal the JSON error response, but in this event just skip
 		// marshalling altogether
diff --git a/vendor/src/github.com/matrix-org/util/json_test.go b/vendor/src/github.com/matrix-org/util/json_test.go
index 0b827245..2248ac3f 100644
--- a/vendor/src/github.com/matrix-org/util/json_test.go
+++ b/vendor/src/github.com/matrix-org/util/json_test.go
@@ -29,12 +29,26 @@ func TestMakeJSONAPI(t *testing.T) {
 		ExpectCode int
 		ExpectJSON string
 	}{
-		{nil, &HTTPError{nil, "Everything is broken", 500}, 500, `{"message":"Everything is broken"}`},         // Error return values
-		{nil, &HTTPError{nil, "Not here", 404}, 404, `{"message":"Not here"}`},                                 // With different status codes
-		{&MockResponse{"yep"}, nil, 200, `{"foo":"yep"}`},                                                      // Success return values
-		{[]MockResponse{{"yep"}, {"narp"}}, nil, 200, `[{"foo":"yep"},{"foo":"narp"}]`},                        // Top-level array success values
-		{[]byte(`actually bytes`), nil, 200, `actually bytes`},                                                 // raw []byte escape hatch
-		{func(cannotBe, marshalled string) {}, nil, 500, `{"message":"Failed to serialise response as JSON"}`}, // impossible marshal
+		// Error message return values
+		{nil, &HTTPError{nil, "Everything is broken", 500, nil}, 500, `{"message":"Everything is broken"}`},
+		// Error JSON return values
+		{nil, &HTTPError{nil, "Everything is broken", 500, struct {
+			Foo string `json:"foo"`
+		}{"yep"}}, 500, `{"foo":"yep"}`},
+		// Error JSON return values which fail to be marshalled should fallback to text
+		{nil, &HTTPError{nil, "Everything is broken", 500, struct {
+			Foo interface{} `json:"foo"`
+		}{func(cannotBe, marshalled string) {}}}, 500, `{"message":"Everything is broken"}`},
+		// With different status codes
+		{nil, &HTTPError{nil, "Not here", 404, nil}, 404, `{"message":"Not here"}`},
+		// Success return values
+		{&MockResponse{"yep"}, nil, 200, `{"foo":"yep"}`},
+		// Top-level array success values
+		{[]MockResponse{{"yep"}, {"narp"}}, nil, 200, `[{"foo":"yep"},{"foo":"narp"}]`},
+		// raw []byte escape hatch
+		{[]byte(`actually bytes`), nil, 200, `actually bytes`},
+		// impossible marshal
+		{func(cannotBe, marshalled string) {}, nil, 500, `{"message":"Failed to serialise response as JSON"}`},
 	}
 
 	for _, tst := range tests {
@@ -58,7 +72,7 @@ func TestMakeJSONAPI(t *testing.T) {
 func TestMakeJSONAPIRedirect(t *testing.T) {
 	log.SetLevel(log.PanicLevel) // suppress logs in test output
 	mock := MockJSONRequestHandler{func(req *http.Request) (interface{}, *HTTPError) {
-		return nil, &HTTPError{nil, "https://matrix.org", 302}
+		return nil, &HTTPError{nil, "https://matrix.org", 302, nil}
 	}}
 	mockReq, _ := http.NewRequest("GET", "http://example.com/foo", nil)
 	mockWriter := httptest.NewRecorder()