diff --git a/esphome/components/api/proto.h b/esphome/components/api/proto.h
index 973395ca65..96d5383ddf 100644
--- a/esphome/components/api/proto.h
+++ b/esphome/components/api/proto.h
@@ -184,6 +184,9 @@ class Proto64Bit {
   const uint64_t value_;
 };
 
+// Forward declaration needed for method declaration
+class ProtoMessage;
+
 class ProtoWriteBuffer {
  public:
   ProtoWriteBuffer(std::vector<uint8_t> *buffer) : buffer_(buffer) {}