diff --git a/src/helpers/ESP32Board.cpp b/src/helpers/ESP32Board.cpp
index a55abb264..d190fca19 100644
--- a/src/helpers/ESP32Board.cpp
+++ b/src/helpers/ESP32Board.cpp
@@ -3,6 +3,10 @@
 #include "ESP32Board.h"
 #include <target.h>
 
+// The RTC backup of ESP32RTCClock, declared in ESP32Board.h.
+RTC_NOINIT_ATTR uint32_t _rtc_backup_time;
+RTC_NOINIT_ATTR uint32_t _rtc_backup_magic;
+
 #if defined(ADMIN_PASSWORD) && !defined(DISABLE_WIFI_OTA)   // Repeater or Room Server only
 #include <WiFi.h>
 #include <AsyncTCP.h>
diff --git a/src/helpers/ESP32Board.h b/src/helpers/ESP32Board.h
index 3f95e6923..cd274cd93 100644
--- a/src/helpers/ESP32Board.h
+++ b/src/helpers/ESP32Board.h
@@ -200,8 +200,11 @@ public:
   }
 };
 
-static RTC_NOINIT_ATTR uint32_t _rtc_backup_time;
-static RTC_NOINIT_ATTR uint32_t _rtc_backup_magic;
+// The time ESP32RTCClock restores after a reset, in RTC memory that a reset does
+// not clear. Defined once, in ESP32Board.cpp: the inline members below run in
+// every translation unit that uses them and must all see the same backup.
+extern uint32_t _rtc_backup_time;
+extern uint32_t _rtc_backup_magic;
 #define RTC_BACKUP_MAGIC  0xAA55CC33
 #define RTC_TIME_MIN      1772323200  // 1 Mar 2026