diff --git a/src/boards/include/boards/pimoroni_pga2350.h b/src/boards/include/boards/pimoroni_pga2350.h
index f4f0a3d2..1bd02dc4 100644
--- a/src/boards/include/boards/pimoroni_pga2350.h
+++ b/src/boards/include/boards/pimoroni_pga2350.h
@@ -20,6 +20,9 @@
 #define PIMORONI_PGA2350
 #define PIMORONI_PGA2350_16MB
 
+// --- RP2350 VARIANT ---
+#define PICO_RP2350A 0
+
 // --- BOARD SPECIFIC ---
 #define PIMORONI_PGA2350_PSRAM_CS_PIN 47
 
diff --git a/src/boards/include/boards/pimoroni_pico_plus2_rp2350.h b/src/boards/include/boards/pimoroni_pico_plus2_rp2350.h
index 34c5fb38..40fff17d 100644
--- a/src/boards/include/boards/pimoroni_pico_plus2_rp2350.h
+++ b/src/boards/include/boards/pimoroni_pico_plus2_rp2350.h
@@ -19,6 +19,9 @@
 // For board detection
 #define PIMORONI_PICO_PLUS2_RP2350
 
+// --- RP2350 VARIANT ---
+#define PICO_RP2350A 0
+
 // --- BOARD SPECIFIC ---
 #define SPCE_SPI 0
 #define SPCE_TX_MISO_PIN 32
diff --git a/src/boards/include/boards/pimoroni_pico_plus2_w_rp2350.h b/src/boards/include/boards/pimoroni_pico_plus2_w_rp2350.h
index ba3c0e56..7a4f1741 100644
--- a/src/boards/include/boards/pimoroni_pico_plus2_w_rp2350.h
+++ b/src/boards/include/boards/pimoroni_pico_plus2_w_rp2350.h
@@ -20,6 +20,9 @@
 // For board detection
 #define PIMORONI_PICO_PLUS2_W_RP2350
 
+// --- RP2350 VARIANT ---
+#define PICO_RP2350A 0
+
 // --- BOARD SPECIFIC ---
 #define PIMORONI_PICO_PLUS2_W_USER_SW_PIN 45
 #define PIMORONI_PICO_PLUS2_W_PSRAM_CS_PIN 47
diff --git a/src/boards/include/boards/seeed_xiao_rp2350.h b/src/boards/include/boards/seeed_xiao_rp2350.h
index 52e16365..69a2ba40 100644
--- a/src/boards/include/boards/seeed_xiao_rp2350.h
+++ b/src/boards/include/boards/seeed_xiao_rp2350.h
@@ -17,6 +17,9 @@
 // For board detection
 #define SEEED_XIAO_RP2350
 
+// --- RP2350 VARIANT ---
+#define PICO_RP2350A 1
+
 //------------- UART -------------//
 #ifndef PICO_DEFAULT_UART
 #define PICO_DEFAULT_UART 0
diff --git a/tools/check_board_header.py b/tools/check_board_header.py
index 4efeef4c..3bfce1c5 100755
--- a/tools/check_board_header.py
+++ b/tools/check_board_header.py
@@ -196,6 +196,7 @@ def read_defines_from(header_file, defines_dict):
 
 if board_header_basename == "amethyst_fpga.h":
     defines['PICO_RP2350'] = DefineType('PICO_RP2350', 1, 1, -1)
+    defines['PICO_RP2350A'] = DefineType('PICO_RP2350A', 0, 0, -1)
 
 with open(board_header) as header_fh:
     last_ifndef = None
@@ -347,7 +348,7 @@ with open(board_header) as header_fh:
                         raise Exception("{}:{}  Include-guard #define {} is missing an #ifndef".format(board_header, lineno, name))
                     if value:
                         raise Exception("{}:{}  Include-guard #define {} shouldn't have a value".format(board_header, lineno, name))
-                    if len(defines) and not (len(defines) == 1 and defines[list(defines.keys())[0]].lineno < 0):
+                    if any(defines[d].lineno >= 0 for d in defines):
                         raise Exception("{}:{}  Include-guard #define {} should be the first define".format(board_header, lineno, name))
                     if name == expected_include_guard:
                         has_include_guard = True
@@ -387,12 +388,15 @@ else:
         other_chip = 'RP2350'
     elif cmake_settings['PICO_PLATFORM'].value == "rp2350":
         other_chip = 'RP2040'
-        if 'PICO_RP2350A' in defines and defines['PICO_RP2350A'].resolved_value == 1:
-            chip = 'RP2350A'
-        else:
-            chip = 'RP2350B'
         if 'PICO_RP2350B' in defines:
             raise Exception("{} sets #define {} {} (should probably be #define {} {})".format(board_header, 'PICO_RP2350B', defines['PICO_RP2350B'].resolved_value, 'PICO_RP2350A', 1 - defines['PICO_RP2350B'].resolved_value))
+        if 'PICO_RP2350A' not in defines:
+            raise Exception("{} has no #define for {} (set to 1 for RP2350A, or 0 for RP2350B)".format(board_header, 'PICO_RP2350A'))
+        else:
+            if defines['PICO_RP2350A'].resolved_value == 1:
+                chip = 'RP2350A'
+            else:
+                chip = 'RP2350B'
         if not board_header.endswith("amethyst_fpga.h"):
             if 'PICO_RP2350_A2_SUPPORTED' not in cmake_default_settings:
                 raise Exception("{} uses chip {} but is missing a pico_cmake_set_default {} comment".format(board_header, chip, 'PICO_RP2350_A2_SUPPORTED'))