diff --git a/esphome/components/api/proto.cpp b/esphome/components/api/proto.cpp
index 6348c74c5f..4f16815d1b 100644
--- a/esphome/components/api/proto.cpp
+++ b/esphome/components/api/proto.cpp
@@ -8,7 +8,7 @@ namespace esphome::api {
 
 static const char *const TAG = "api.proto";
 
-uint32_t ProtoSize::varint_slow_(uint32_t value) {
+uint32_t ProtoSize::varint_slow(uint32_t value) {
   // value is guaranteed >= 128 here (fast path handled inline)
   if (value < 16384) {
     return 2;  // 14 bits
diff --git a/esphome/components/api/proto.h b/esphome/components/api/proto.h
index 2ac8dbd844..ec49964035 100644
--- a/esphome/components/api/proto.h
+++ b/esphome/components/api/proto.h
@@ -524,10 +524,10 @@ class ProtoSize {
         return 4;
       return 5;
     }
-    return varint_slow_(value);
+    return varint_slow(value);
   }
   // Slow path for varint >= 128, outlined to keep fast path small
-  static uint32_t varint_slow_(uint32_t value) __attribute__((noinline));
+  static uint32_t varint_slow(uint32_t value) __attribute__((noinline));
 
   /**
    * @brief Calculates the size in bytes needed to encode a uint64_t value as a varint