diff --git a/.gitignore b/.gitignore
index b63315e9..bcb556b3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@ ph_*/
 *bios.bin
 /m2ctx
 *.sav
+_gen_externs_tmp*
diff --git a/tools/gen_externs.py b/tools/gen_externs.py
index 87a9a802..b1d450f8 100644
--- a/tools/gen_externs.py
+++ b/tools/gen_externs.py
@@ -9,40 +9,105 @@ import sys
 def eprint(*args, **kwargs):
     print(*args, file=sys.stderr, **kwargs)
 
-parser = argparse.ArgumentParser(description='Generates .inc files with all necessary external symbols')
-parser.add_argument('file', help='Assembly source file')
+parser = argparse.ArgumentParser(description='Generates .inc files with external symbols used by Assembly code')
+parser.add_argument('files', nargs='+', help='.s file to generate .inc file for')
+
+args = parser.parse_args()
 
 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
-include_dir = root_dir / 'asm'
+asm_dir = root_dir / 'asm'
+tmp_file = '_gen_externs_tmp'
+tmp_obj_file = f'{tmp_file}.o'
+tmp_asm_file = f'{tmp_file}.s'
 
-if platform.system() == 'Windows': _as = [str(as_path)]
-else: _as = ['wine', str(as_path)]
+if platform.system() == 'Windows': as_cmd = [str(as_path)]
+else: as_cmd = ['wine', str(as_path)]
 
-args = parser.parse_args()
-
-_as.extend([
+as_cmd.extend([
     '-nolink',
     '-proc', 'arm5te',
     '-msgstyle', 'gcc',
-    '-dis',
-    f'-I{include_dir}',
-    args.file
+    '-DEUR', '-DUSA',
+    '-o', tmp_obj_file,
+    f'-I{asm_dir}',
 ])
 
-try:
-    output = subprocess.check_output(_as, stderr=subprocess.DEVNULL)
-except subprocess.CalledProcessError as e:
-    output = e.stdout.decode()
+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()
 
-symbols: list[str] = re.findall(r'Unknown identifier, (?:[\r\n]+\S+ )?(\S+)', output)
-if len(symbols) == 0:
-    eprint("No symbols needed")
-    exit(0)
+    # Get unknown identifiers
+    symbols: list[str] = re.findall(r'Unknown identifier, (?:[\r\n]+\S+ )?(\S+)', output)
+    if len(symbols) == 0:
+        return []
+    
+    return symbols
 
-print('#pragma once')
-for i, symbol in enumerate(symbols):
-    # Avoid duplicates
-    if symbol in symbols[:i]: continue
-    print(f'.extern {symbol}')
+files_updated = 0
+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
+
+    # 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:
+        for line in lines:
+            f.write(line)
+            f.write('\n')
+    symbols = get_unknown_symbols(tmp_asm_file)
+    os.remove(tmp_asm_file)
+
+    # Create inc file
+    if len(symbols) > 0:
+        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
+
+
+for file in args.files:
+    if not file.endswith('.s'): continue
+    path = Path(file)
+    print(path)
+    generate_externs(path)
+    files_updated += 1
+
+print(f"Updated {files_updated} file(s)")
+print(f"Created {inc_files_created} .inc file(s)")