diff --git a/cores/esp32/io_pin_remap.h b/cores/esp32/io_pin_remap.h
index 4a23de4a829..cd5c93f8737 100644
--- a/cores/esp32/io_pin_remap.h
+++ b/cores/esp32/io_pin_remap.h
@@ -18,7 +18,7 @@ int8_t digitalPinFromGPIONumber(int8_t gpioPin);
 #define pulseInLong(pin, state, timeout)    pulseInLong(digitalPinToGPIONumber(pin), state, timeout)
 #define pulseIn(pin, state, timeout)        pulseIn(digitalPinToGPIONumber(pin), state, timeout)
 #define noTone(_pin)                        noTone(digitalPinToGPIONumber(_pin))
-#define tone(_pin, frequency, duration)     tone(digitalPinToGPIONumber(_pin), frequency, duration)
+#define tone(_pin, args...)                 tone(digitalPinToGPIONumber(_pin), args)
 
 // cores/esp32/esp32-hal.h
 #define analogGetChannel(pin)       analogGetChannel(digitalPinToGPIONumber(pin))
diff --git a/tools/platformio-build.py b/tools/platformio-build.py
index 2ee2d92894f..bc57256114a 100644
--- a/tools/platformio-build.py
+++ b/tools/platformio-build.py
@@ -171,6 +171,10 @@ def add_tinyuf2_extra_image():
 # Target: Build Core Library
 #
 
+# Set -DARDUINO_CORE_BUILD only for the core library
+corelib_env = env.Clone()
+corelib_env.Append(CPPDEFINES=["ARDUINO_CORE_BUILD"])
+
 libs = []
 
 variants_dir = join(FRAMEWORK_DIR, "variants")
@@ -180,13 +184,14 @@ def add_tinyuf2_extra_image():
 
 if "build.variant" in board_config:
     env.Append(CPPPATH=[join(variants_dir, board_config.get("build.variant"))])
-    env.BuildSources(
+    corelib_env.Append(CPPPATH=[join(variants_dir, board_config.get("build.variant"))])
+    corelib_env.BuildSources(
         join("$BUILD_DIR", "FrameworkArduinoVariant"),
         join(variants_dir, board_config.get("build.variant")),
     )
 
 libs.append(
-    env.BuildLibrary(
+    corelib_env.BuildLibrary(
         join("$BUILD_DIR", "FrameworkArduino"),
         join(FRAMEWORK_DIR, "cores", board_config.get("build.core")),
     )
diff --git a/variants/arduino_nano_nora/io_pin_remap.cpp b/variants/arduino_nano_nora/io_pin_remap.cpp
index e53c500a328..2a18e029df2 100644
--- a/variants/arduino_nano_nora/io_pin_remap.cpp
+++ b/variants/arduino_nano_nora/io_pin_remap.cpp
@@ -1,4 +1,20 @@
-#ifndef BOARD_USES_HW_GPIO_NUMBERS
+#if defined(BOARD_HAS_PIN_REMAP) && !defined(ARDUINO_CORE_BUILD)
+// -DARDUINO_CORE_BUILD must be set for core files only, to avoid extra
+// remapping steps that would create all sorts of issues in the core.
+// Removing -DBOARD_HAS_PIN_REMAP at least does correctly restore the
+// use of GPIO numbers in the API.
+#error This build system is not supported. Please rebuild without BOARD_HAS_PIN_REMAP.
+#endif
+
+#if !defined(BOARD_HAS_PIN_REMAP)
+// This board uses pin mapping but the build system has disabled it
+#warning The build system forces the Arduino API to use GPIO numbers on a board that has custom pin mapping.
+#elif defined(BOARD_USES_HW_GPIO_NUMBERS)
+// The user has chosen to disable pin mappin.
+#warning The Arduino API will use GPIO numbers for this build.
+#endif
+
+#if defined(BOARD_HAS_PIN_REMAP) && !defined(BOARD_USES_HW_GPIO_NUMBERS)
 
 #include "Arduino.h"