diff --git a/.gitignore b/.gitignore
index bcb556b3..b63315e9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,4 +5,3 @@ ph_*/
 *bios.bin
 /m2ctx
 *.sav
-_gen_externs_tmp*
diff --git a/Makefile b/Makefile
index 8dedf701..85bd8cb1 100644
--- a/Makefile
+++ b/Makefile
@@ -25,6 +25,7 @@ ASSETS_TXT := assets.txt
 ASM_FILES := $(shell find asm -name *.s)
 CXX_FILES := $(shell find src -name *.cpp)
 ASM_OBJS = $(ASM_FILES:%.s=$(TARGET_DIR)/%.s.o)
+ASM_INCS = $(ASM_FILES:%.s=%.inc)
 CXX_OBJS = $(CXX_FILES:%.cpp=$(TARGET_DIR)/%.cpp.o)
 
 OV_BINS := $(wildcard $(TARGET_DIR)/overlays/*.bin)
@@ -58,6 +59,7 @@ help:
 	@echo "make eur ........................ Builds European ROM"
 	@echo "make usa ........................ Builds American ROM"
 	@echo "make clean ...................... Clean up build files"
+	@echo "make gen_externs ................ Generates .inc files for Assembly"
 
 .PHONY: eur
 eur:
@@ -128,3 +130,9 @@ compress: $(OV_LZS)
 
 $(OV_LZS): %.lz: %.bin
 	$(TOOLS_DIR)/compress/compress -p -i $< -o $@
+
+.PHONY: gen_externs
+gen_externs: $(ASM_INCS)
+
+$(ASM_INCS): %.inc: %.s
+	python $(TOOLS_DIR)/gen_externs.py $<
diff --git a/tools/gen_externs.py b/tools/gen_externs.py
index 192e7eee..2845502e 100644
--- a/tools/gen_externs.py
+++ b/tools/gen_externs.py
@@ -2,9 +2,9 @@ import argparse
 import os
 from pathlib import Path
 import platform
-import re
 import subprocess
 import sys
+import tempfile
 
 def eprint(*args, **kwargs):
     print(*args, file=sys.stderr, **kwargs)
@@ -18,11 +18,9 @@ tools_dir = Path(os.path.dirname(os.path.realpath(__file__)))
 as_path = tools_dir / 'mwccarm' / '2.0' / 'sp1p5' / 'mwasmarm.exe'
 root_dir = tools_dir.parent
 asm_dir = root_dir / 'asm'
-tmp_file = '_gen_externs_tmp'
-tmp_obj_file = f'{tmp_file}.o'
-tmp_asm_file = f'{tmp_file}.s'
 
 MSG_UNKNOWN_IDENTIFIER = 'Unknown identifier,'
+MSG_DUPLICATE_DECLARATION = 'Incompatible duplicate declaration of'
 
 if platform.system() == 'Windows': as_cmd = [str(as_path)]
 else: as_cmd = ['wine', str(as_path)]
@@ -32,39 +30,45 @@ as_cmd.extend([
     '-proc', 'arm5te',
     '-msgstyle', 'gcc',
     '-DEUR', '-DUSA',
-    '-o', tmp_obj_file,
     f'-I{asm_dir}',
 ])
 
 def get_unknown_symbols(file: Path):
-    # Run assembler
-    cmd = as_cmd.copy()
-    cmd.append(str(file))
-    try:
-        output = subprocess.check_output(cmd, stderr=subprocess.DEVNULL)
-        output = output.decode()
-        os.remove(tmp_obj_file)
-    except subprocess.CalledProcessError as e:
-        output = e.stdout.decode()
+    with tempfile.NamedTemporaryFile(delete=True) as tmp_obj_file:
+        # Run assembler
+        cmd = as_cmd.copy()
+        cmd.extend(['-o', tmp_obj_file.name])
+        cmd.append(str(file))
+        try:
+            output = subprocess.check_output(cmd, stderr=subprocess.DEVNULL)
+            output = output.decode()
+        except subprocess.CalledProcessError as e:
+            output = e.stdout.decode()
 
-    # Get unknown identifiers
-    lines = output.splitlines()
-    symbol = ''
-    symbols: list[str] = []
-    for line in lines:
-        if not line.startswith(tmp_asm_file): continue
-        if ':' not in line: continue
-        line = line[line.index(':', len(tmp_asm_file) + 1) + 1:].strip()
-        if line.startswith(MSG_UNKNOWN_IDENTIFIER):
-            if symbol != '': symbols.append(symbol)
-            symbol = line[len(MSG_UNKNOWN_IDENTIFIER):].strip()
-        else:
-            symbol += line.strip()
-    if symbol != '': symbols.append(symbol)
-    if len(symbols) == 0:
-        return []
+        # Get unknown identifiers
+        lines = output.splitlines()
+        symbol = ''
+        symbols: set[str] = set()
+        skip = False
+        for line in lines:
+            # print(line)
+            if ':' not in line: continue
+            line = line.rsplit(':', 1)[-1].strip()
+            if line.startswith(MSG_DUPLICATE_DECLARATION):
+                symbols.add(symbol)
+                skip = True
+            elif line.startswith(MSG_UNKNOWN_IDENTIFIER):
+                symbols.add(symbol)
+                skip = False
+                symbol = line[len(MSG_UNKNOWN_IDENTIFIER):].strip()
+            elif not skip:
+                symbol += line.strip()
+        symbols.add(symbol)
+        symbols.remove('')
+        if len(symbols) == 0:
+            return []
     
-    return sorted(symbols)
+    return sorted(list(symbols))
 
 files_updated = 0
 inc_files_created = 0
@@ -72,56 +76,57 @@ inc_files_created = 0
 def generate_externs(file: Path):
     global inc_files_created
 
-    file_name = file.name.rsplit('.', 1)[0]
-    inc_file_name = f'{file_name}.inc'
-    inc_path = file.parent / 'include' / inc_file_name
+    with tempfile.NamedTemporaryFile('w', suffix='.s', delete=True, encoding='Shift-JIS') as tmp_asm_file:
+        file_name = file.name.rsplit('.', 1)[0]
+        inc_file_name = f'{file_name}.inc'
+        inc_path = file.parent / inc_file_name
 
-    # Comment out '.include ".../my_file.inc"
-    with open(file, 'r', encoding='Shift-JIS') as f:
-        contents = f.read()
-    lines = contents.splitlines()
-    has_inc_file = False
-    for i in range(len(lines)):
-        if not lines[i].strip().startswith('.include'): continue
-        if inc_file_name not in lines[i]: continue
-        lines[i] = f';{lines[i]}'
-        has_inc_file = True
-        break
-    
-    # Get unknown symbols
-    with open(f'{tmp_file}.s', 'w', encoding='Shift-JIS') as f:
+        # Comment out '.include ".../my_file.inc"
+        with open(file, 'r', encoding='Shift-JIS') as f:
+            contents = f.read()
+        lines = contents.splitlines()
+        has_inc_file = False
+        for i in range(len(lines)):
+            if not lines[i].strip().startswith('.include'): continue
+            if inc_file_name not in lines[i]: continue
+            lines[i] = f';{lines[i]}'
+            has_inc_file = True
+            break
+        
+        # Get unknown symbols
         for line in lines:
-            f.write(line)
-            f.write('\n')
-    symbols = get_unknown_symbols(tmp_asm_file)
-    os.remove(tmp_asm_file)
+            tmp_asm_file.write(line)
+            tmp_asm_file.write('\n')
+        tmp_asm_file.flush()
+        symbols = get_unknown_symbols(tmp_asm_file.name)
 
-    # Create inc file
-    if len(symbols) > 0:
+        # Create inc file
         with open(inc_path, 'w') as f:
             f.write('#pragma once\n')
             for i, symbol in enumerate(symbols):
                 # Skip duplicates
                 if symbol in symbols[:i]: continue
                 f.write(f'.extern {symbol}\n')
-    
-    # Add .include
-    if not has_inc_file and len(symbols) > 0:
-        relative_inc_path = inc_path.relative_to('asm/')
-        lines.insert(0, f'    .include "{relative_inc_path}"')
-        with open(file, 'w', encoding='Shift-JIS') as f:
-            for line in lines:
-                f.write(line)
-                f.write('\n')
-        inc_files_created += 1
+        
+        # Add .include
+        if not has_inc_file:
+            relative_inc_path = inc_path.relative_to('asm/')
+            lines.insert(0, f'    .include "{relative_inc_path}"')
+            with open(file, 'w', encoding='Shift-JIS') as f:
+                for line in lines:
+                    f.write(line)
+                    f.write('\n')
+            inc_files_created += 1
 
 
 for file in args.files:
     if not file.endswith('.s'): continue
     path = Path(file)
-    print(path)
+    if len(args.files) > 1:
+        print(path)
     generate_externs(path)
     files_updated += 1
 
-print(f"Updated {files_updated} file(s)")
-print(f"Created {inc_files_created} .inc file(s)")
+if len(args.files) > 1:
+    print(f"Updated {files_updated} file(s)")
+    print(f"Created {inc_files_created} .inc file(s)")