diff --git a/configs/esp32-core/include/board.h b/configs/esp32-core/include/board.h
index fb0c327482..45e3d109af 100644
--- a/configs/esp32-core/include/board.h
+++ b/configs/esp32-core/include/board.h
@@ -50,15 +50,22 @@
 #endif
 
 /* Clock reconfiguration is currently disabled, so the CPU will be running
- * at the XTAL frequency.
+ * at the XTAL frequency or at two times the XTAL frequency, depending upon
+ * how we load the code:
+ *
+ * - If we load the code into FLASH at address 0x1000 where it is started by
+ *   the second level bootloader, then the frequency is the crystal
+ *   frequency.
+ * - If we load the code into IRAM after the second level bootloader has run
+ *   this frequency will be  twice the crystal frequency.
+ *
+ * Don't ask me for an explanation.
  */
 
-#if 0
-#  define BOARD_CLOCK_FREQUENCY 80000000
-#else
-  /* Hmmm... actually appears to be running at about 2 x the XTAL frequency */
-
+#ifdef CONFIG_ESP32CORE_RUN_IRAM
 #  define BOARD_CLOCK_FREQUENCY (2 * BOARD_XTAL_FREQUENCY)
+#else
+#  define BOARD_CLOCK_FREQUENCY BOARD_XTAL_FREQUENCY
 #endif
 
 #endif /* __CONFIGS_ESP32_CORE_INCLUDE_BOARD_H */