diff --git a/esphome/components/modbus/modbus.h b/esphome/components/modbus/modbus.h
index 91fc55b998..876c46b688 100644
--- a/esphome/components/modbus/modbus.h
+++ b/esphome/components/modbus/modbus.h
@@ -36,6 +36,8 @@ class Modbus : public uart::UARTDevice, public Component {
   std::vector<ModbusDevice *> devices_;
 };
 
+uint16_t crc16(const uint8_t *data, uint8_t len);
+
 class ModbusDevice {
  public:
   void set_parent(Modbus *parent) { parent_ = parent; }