diff --git a/esphome/components/api/proto.cpp b/esphome/components/api/proto.cpp
index 4f5b3f0918f..6e348dde44e 100644
--- a/esphome/components/api/proto.cpp
+++ b/esphome/components/api/proto.cpp
@@ -11,13 +11,15 @@ static const char *const TAG = "api.proto";
 uint32_t ProtoSize::varint_slow(uint32_t value) { return varint_wide(value); }
 
 void ProtoWriteBuffer::encode_varint_raw_slow_(uint32_t value) {
+  // Use __restrict__ so the compiler knows pos doesn't alias this->
+  // and can keep it in a register across the loop.
+  uint8_t *__restrict__ pos = this->pos_;
   do {
-    this->debug_check_bounds_(1);
-    *this->pos_++ = static_cast<uint8_t>(value | 0x80);
+    *pos++ = static_cast<uint8_t>(value | 0x80);
     value >>= 7;
   } while (value > 0x7F);
-  this->debug_check_bounds_(1);
-  *this->pos_++ = static_cast<uint8_t>(value);
+  *pos++ = static_cast<uint8_t>(value);
+  this->pos_ = pos;
 }
 
 ProtoVarIntResult ProtoVarInt::parse_slow(const uint8_t *buffer, uint32_t len) {