diff --git a/esphome/components/api/proto.cpp b/esphome/components/api/proto.cpp
index dd682fddd4..7e01185849 100644
--- a/esphome/components/api/proto.cpp
+++ b/esphome/components/api/proto.cpp
@@ -20,7 +20,7 @@ void ProtoWriteBuffer::encode_varint_raw_slow_(uint32_t value) {
   *this->pos_++ = static_cast<uint8_t>(value);
 }
 
-ProtoVarIntResult ProtoVarInt::parse_slow_(const uint8_t *buffer, uint32_t len) {
+ProtoVarIntResult ProtoVarInt::parse_slow(const uint8_t *buffer, uint32_t len) {
   // Multi-byte varint: first byte already checked to have high bit set
   uint32_t result32 = buffer[0] & 0x7F;
 #ifdef USE_API_VARINT64
@@ -36,14 +36,14 @@ ProtoVarIntResult ProtoVarInt::parse_slow_(const uint8_t *buffer, uint32_t len)
     }
   }
 #ifdef USE_API_VARINT64
-  return parse_wide_(buffer, len, result32);
+  return parse_wide(buffer, len, result32);
 #else
   return {0, 0};
 #endif
 }
 
 #ifdef USE_API_VARINT64
-ProtoVarIntResult ProtoVarInt::parse_wide_(const uint8_t *buffer, uint32_t len, uint32_t result32) {
+ProtoVarIntResult ProtoVarInt::parse_wide(const uint8_t *buffer, uint32_t len, uint32_t result32) {
   uint64_t result64 = result32;
   uint32_t limit = std::min(len, uint32_t(10));
   for (uint32_t i = 4; i < limit; i++) {
diff --git a/esphome/components/api/proto.h b/esphome/components/api/proto.h
index 2cd8f286b2..04cb0cc85c 100644
--- a/esphome/components/api/proto.h
+++ b/esphome/components/api/proto.h
@@ -98,17 +98,20 @@ inline void encode_varint_to_buffer(uint32_t val, uint8_t *buffer) {
  * within the same function scope where temporaries are created.
  */
 
+/// Sentinel value for consumed field indicating parse failure
+inline constexpr uint32_t PROTO_VARINT_PARSE_FAILED = 0;
+
 /// Result of parsing a varint: value + number of bytes consumed.
-/// consumed == 0 indicates parse failure (not enough data or invalid).
+/// consumed == PROTO_VARINT_PARSE_FAILED indicates parse failure (not enough data or invalid).
 struct ProtoVarIntResult {
 #ifdef USE_API_VARINT64
   uint64_t value;
 #else
   uint32_t value;
 #endif
-  uint32_t consumed;  // 0 = parse failed
+  uint32_t consumed;  // PROTO_VARINT_PARSE_FAILED = parse failed
 
-  constexpr bool has_value() const { return this->consumed != 0; }
+  constexpr bool has_value() const { return this->consumed != PROTO_VARINT_PARSE_FAILED; }
   constexpr uint16_t as_uint16() const { return this->value; }
   constexpr uint32_t as_uint32() const { return this->value; }
   constexpr bool as_bool() const { return this->value; }
@@ -135,17 +138,16 @@ class ProtoVarInt {
     // (booleans, small enums, field tags, small message sizes/types).
     if ((buffer[0] & 0x80) == 0) [[likely]]
       return {buffer[0], 1};
-    return parse_slow_(buffer, len);
+    return parse_slow(buffer, len);
   }
 
  protected:
   // Slow path for multi-byte varints (>= 128), outlined to keep fast path small
-  static ProtoVarIntResult parse_slow_(const uint8_t *buffer, uint32_t len) __attribute__((noinline));
+  static ProtoVarIntResult parse_slow(const uint8_t *buffer, uint32_t len) __attribute__((noinline));
 
 #ifdef USE_API_VARINT64
   /// Continue parsing varint bytes 4-9 with 64-bit arithmetic.
-  static ProtoVarIntResult parse_wide_(const uint8_t *buffer, uint32_t len, uint32_t result32)
-      __attribute__((noinline));
+  static ProtoVarIntResult parse_wide(const uint8_t *buffer, uint32_t len, uint32_t result32) __attribute__((noinline));
 #endif
 
  public: