diff --git a/handler.go b/handler.go
index 8b2a709..2673f35 100644
--- a/handler.go
+++ b/handler.go
@@ -36,8 +36,8 @@ func DecodeParams[T any](p RawParams) (T, error) {
 
 // methodHandler is a handler for a single method
 type methodHandler struct {
-	paramReceivers []reflect.Type
-	nParams        int
+	paramReceivers       []reflect.Type
+	reqParams, optParams int
 
 	receiver    reflect.Value
 	handlerFunc reflect.Value
@@ -144,30 +144,34 @@ func (s *handler) register(namespace string, r interface{}) {
 	for i := 0; i < val.NumMethod(); i++ {
 		method := val.Type().Method(i)
 
-		funcType := method.Func.Type()
 		hasCtx := 0
-		if funcType.NumIn() >= 2 && funcType.In(1) == contextType {
+		if method.Type.NumIn() >= 2 && method.Type.In(1) == contextType {
 			hasCtx = 1
 		}
 
 		hasRawParams := false
-		ins := funcType.NumIn() - 1 - hasCtx
+		ins := method.Type.NumIn() - 1 - hasCtx
+		opt := 0
 		recvs := make([]reflect.Type, ins)
 		for i := 0; i < ins; i++ {
 			if hasRawParams && i > 0 {
 				panic("raw params must be the last parameter")
 			}
-			if funcType.In(i+1+hasCtx) == rtRawParams {
+			if method.Type.In(i+1+hasCtx) == rtRawParams {
 				hasRawParams = true
 			}
 			recvs[i] = method.Type.In(i + 1 + hasCtx)
+			if recvs[i].Kind() == reflect.Pointer {
+				opt++
+			}
 		}
 
-		valOut, errOut, _ := processFuncOut(funcType)
+		valOut, errOut, _ := processFuncOut(method.Type)
 
 		s.methods[namespace+"."+method.Name] = methodHandler{
 			paramReceivers: recvs,
-			nParams:        ins,
+			reqParams:      ins - opt,
+			optParams:      opt,
 
 			handlerFunc: method.Func,
 			receiver:    val,
@@ -361,7 +365,7 @@ func (s *handler) handle(ctx context.Context, req request, w func(func(io.Writer
 		return
 	}
 
-	callParams := make([]reflect.Value, 1+handler.hasCtx+handler.nParams)
+	callParams := make([]reflect.Value, 1+handler.hasCtx+handler.reqParams+handler.optParams)
 	callParams[0] = handler.receiver
 	if handler.hasCtx == 1 {
 		callParams[1] = reflect.ValueOf(ctx)
@@ -385,21 +389,30 @@ func (s *handler) handle(ctx context.Context, req request, w func(func(io.Writer
 			}
 		}
 
-		if len(ps) != handler.nParams {
-			rpcError(w, &req, rpcInvalidParams, fmt.Errorf("wrong param count (method '%s'): %d != %d", req.Method, len(ps), handler.nParams))
+		if len(ps) > handler.reqParams+handler.optParams || len(ps) < handler.reqParams {
+			var err error
+			if handler.optParams > 0 {
+				err = fmt.Errorf("wrong param count %d (method '%s'): expected %d - %d",
+					len(ps), req.Method, handler.reqParams,
+					handler.reqParams+handler.optParams,
+				)
+			} else {
+				err = fmt.Errorf("wrong param count %d (method '%s'): expected %d", len(ps), req.Method, handler.reqParams)
+			}
+			rpcError(w, &req, rpcInvalidParams, err)
 			stats.Record(ctx, metrics.RPCRequestError.M(1))
 			done(false)
 			return
 		}
 
-		for i := 0; i < handler.nParams; i++ {
+		for i, p := range ps {
 			var rp reflect.Value
 
 			typ := handler.paramReceivers[i]
 			dec, found := s.paramDecoders[typ]
 			if !found {
 				rp = reflect.New(typ)
-				if err := json.NewDecoder(bytes.NewReader(ps[i].data)).Decode(rp.Interface()); err != nil {
+				if err := json.NewDecoder(bytes.NewReader(p.data)).Decode(rp.Interface()); err != nil {
 					rpcError(w, &req, rpcParseError, xerrors.Errorf("unmarshaling params for '%s' (param: %T): %w", req.Method, rp.Interface(), err))
 					stats.Record(ctx, metrics.RPCRequestError.M(1))
 					return
@@ -407,7 +420,7 @@ func (s *handler) handle(ctx context.Context, req request, w func(func(io.Writer
 				rp = rp.Elem()
 			} else {
 				var err error
-				rp, err = dec(ctx, ps[i].data)
+				rp, err = dec(ctx, p.data)
 				if err != nil {
 					rpcError(w, &req, rpcParseError, xerrors.Errorf("decoding params for '%s' (param: %d; custom decoder): %w", req.Method, i, err))
 					stats.Record(ctx, metrics.RPCRequestError.M(1))
diff --git a/rpc_test.go b/rpc_test.go
index 73bd9c1..df105aa 100644
--- a/rpc_test.go
+++ b/rpc_test.go
@@ -318,7 +318,7 @@ func TestRPC(t *testing.T) {
 	require.NoError(t, err)
 
 	_, err = erronly.AddGet()
-	if err == nil || err.Error() != "RPC error (-32602): wrong param count (method 'SimpleServerHandler.AddGet'): 0 != 1" {
+	if err == nil || err.Error() != "RPC error (-32602): wrong param count 0 (method 'SimpleServerHandler.AddGet'): expected 1" {
 		t.Error("wrong error:", err)
 	}
 	closer()
@@ -429,7 +429,7 @@ func TestRPCHttpClient(t *testing.T) {
 	require.NoError(t, err)
 
 	_, err = erronly.AddGet()
-	if err == nil || err.Error() != "RPC error (-32602): wrong param count (method 'SimpleServerHandler.AddGet'): 0 != 1" {
+	if err == nil || err.Error() != "RPC error (-32602): wrong param count 0 (method 'SimpleServerHandler.AddGet'): expected 1" {
 		t.Error("wrong error:", err)
 	}
 	closer()