diff --git a/esphome/components/api/api_frame_helper_plaintext.cpp b/esphome/components/api/api_frame_helper_plaintext.cpp
index 59daf49bfc..859bb26630 100644
--- a/esphome/components/api/api_frame_helper_plaintext.cpp
+++ b/esphome/components/api/api_frame_helper_plaintext.cpp
@@ -201,19 +201,20 @@ APIError APIPlaintextFrameHelper::read_packet(ReadPacketBuffer *buffer) {
       // We must send at least 3 bytes to be read, so we add
       // a message after the indicator byte to ensures its long
       // enough and can aid in debugging.
+      static constexpr uint8_t INDICATOR_MSG_SIZE = 19;
 #ifdef USE_ESP8266
-      static const char msg_progmem[] PROGMEM = "\x00"
+      static const char MSG_PROGMEM[] PROGMEM = "\x00"
                                                 "Bad indicator byte";
-      char msg[19];
-      memcpy_P(msg, msg_progmem, 19);
+      char msg[INDICATOR_MSG_SIZE];
+      memcpy_P(msg, MSG_PROGMEM, INDICATOR_MSG_SIZE);
       iov[0].iov_base = (void *) msg;
 #else
-      static const char msg[] = "\x00"
+      static const char MSG[] = "\x00"
                                 "Bad indicator byte";
-      iov[0].iov_base = (void *) msg;
+      iov[0].iov_base = (void *) MSG;
 #endif
-      iov[0].iov_len = 19;
-      this->write_raw_(iov, 1, 19);
+      iov[0].iov_len = INDICATOR_MSG_SIZE;
+      this->write_raw_(iov, 1, INDICATOR_MSG_SIZE);
     }
     return aerr;
   }