diff --git a/esphome/core/bytebuffer.cpp b/esphome/core/bytebuffer.cpp
index 5d5323d875..75806fad32 100644
--- a/esphome/core/bytebuffer.cpp
+++ b/esphome/core/bytebuffer.cpp
@@ -81,12 +81,25 @@ void ByteBuffer::flip() {
   this->position_ = 0;
 }
 
+bool ByteBuffer::is_changed() {
+  bool changed = this->is_changed_;
+  this->is_changed_ = false;
+  return changed;
+}
+
+void ByteBuffer::update_used_space_() {
+  this->is_changed_ = true;
+  if (this->used_space_ < this->position_) {
+    this->resize();
+  }
+}
+
 /// Getters
 uint8_t ByteBuffer::get_uint8() {
   assert(this->get_remaining() >= 1);
   this->position_++;
-  this->update_();
-  return this->data_[this->position_];
+  this->update_used_space_();
+  return this->data_[this->position_ - 1];
 }
 uint64_t ByteBuffer::get_uint(size_t length) {
   assert(this->get_remaining() >= length);
@@ -104,7 +117,7 @@ uint64_t ByteBuffer::get_uint(size_t length) {
       value |= this->data_[this->position_++];
     }
   }
-  this->update_();
+  this->update_used_space_();
   return value;
 }
 
@@ -128,7 +141,7 @@ std::vector<uint8_t> ByteBuffer::get_vector(size_t length) {
   assert(this->get_remaining() >= length);
   auto start = this->data_.begin() + this->position_;
   this->position_ += length;
-  this->update_();
+  this->update_used_space_();
   return {start, start + length};
 }
 void ByteBuffer::get_bytes(uint8_t *value, size_t length) {
@@ -137,14 +150,14 @@ void ByteBuffer::get_bytes(uint8_t *value, size_t length) {
   while (length-- != 0) {
     *(value + index++) = this->data_[this->position_++];
   }
-  this->update_();
+  this->update_used_space_();
 }
 
 /// Putters
 void ByteBuffer::put_uint8(uint8_t value) {
   assert(this->get_remaining() >= 1);
   this->data_[this->position_++] = value;
-  this->update_();
+  this->update_used_space_();
 }
 
 void ByteBuffer::put_uint(uint64_t value, size_t length) {
@@ -162,7 +175,7 @@ void ByteBuffer::put_uint(uint64_t value, size_t length) {
       value >>= 8;
     }
   }
-  this->update_();
+  this->update_used_space_();
 }
 void ByteBuffer::put_float(float value) {
   static_assert(sizeof(float) == sizeof(uint32_t), "Float sizes other than 32 bit not supported");
@@ -178,7 +191,7 @@ void ByteBuffer::put_vector(const std::vector<uint8_t> &value) {
   assert(this->get_remaining() >= value.size());
   std::copy(value.begin(), value.end(), this->data_.begin() + this->position_);
   this->position_ += value.size();
-  this->update_();
+  this->update_used_space_();
 }
 void ByteBuffer::put_bytes(const uint8_t *value, size_t length) {
   assert(this->get_remaining() >= length);
@@ -186,7 +199,7 @@ void ByteBuffer::put_bytes(const uint8_t *value, size_t length) {
   while (length-- != 0) {
     this->data_[this->position_++] = static_cast<uint8_t>(*(value + index++));
   }
-  this->update_();
+  this->update_used_space_();
 }
 
 }  // namespace esphome
diff --git a/esphome/core/bytebuffer.h b/esphome/core/bytebuffer.h
index 4662195fb4..50dd10250d 100644
--- a/esphome/core/bytebuffer.h
+++ b/esphome/core/bytebuffer.h
@@ -139,11 +139,7 @@ class ByteBuffer {
   void reset() { this->position_ = this->mark_; }
   void resize() { this->used_space_ = this->position_; }
 
-  bool is_changed() {
-    bool changed = this->is_changed_;
-    this->is_changed_ = false;
-    return changed;
-  }
+  bool is_changed();
 
   ByteBuffer &operator[](size_t idx) {
     this->set_position(idx);
@@ -152,12 +148,8 @@ class ByteBuffer {
 
  protected:
   ByteBuffer(std::vector<uint8_t> const &data) : data_(data), limit_(data.size()) {}
-  void update_() {
-    this->is_changed_ = true;
-    if (this->used_space_ < this->position_) {
-      this->resize();
-    }
-  }
+  void update_used_space_();
+
   std::vector<uint8_t> data_;
   Endian endianness_{LITTLE};
   size_t position_{0};