diff --git a/python/build/autotools.py b/python/build/autotools.py
index d121bf6bf..f8c4f42c4 100644
--- a/python/build/autotools.py
+++ b/python/build/autotools.py
@@ -2,6 +2,7 @@ import os.path, subprocess, sys
 from typing import Collection, Iterable, Optional
 
 from build.makeproject import MakeProject
+from .toolchain import AnyToolchain
 
 class AutotoolsProject(MakeProject):
     def __init__(self, url: str, md5: str, installed: str,
@@ -22,7 +23,7 @@ class AutotoolsProject(MakeProject):
         self.libs = libs
         self.subdirs = subdirs
 
-    def configure(self, toolchain) -> str:
+    def configure(self, toolchain: AnyToolchain) -> str:
         src = self.unpack(toolchain)
         if self.autogen:
             if sys.platform == 'darwin':
@@ -70,7 +71,7 @@ class AutotoolsProject(MakeProject):
 
         return build
 
-    def _build(self, toolchain) -> None:
+    def _build(self, toolchain: AnyToolchain) -> None:
         build = self.configure(toolchain)
         if self.subdirs is not None:
             for subdir in self.subdirs:
diff --git a/python/build/cmake.py b/python/build/cmake.py
index def58c65d..a26d7d6f8 100644
--- a/python/build/cmake.py
+++ b/python/build/cmake.py
@@ -5,6 +5,7 @@ from typing import Optional, TextIO
 from collections.abc import Mapping
 
 from build.project import Project
+from .toolchain import AnyToolchain
 
 def __write_cmake_compiler(f: TextIO, language: str, compiler: str) -> None:
     s = compiler.split(' ', 1)
@@ -13,7 +14,7 @@ def __write_cmake_compiler(f: TextIO, language: str, compiler: str) -> None:
         compiler = s[1]
     print(f'set(CMAKE_{language}_COMPILER {compiler})', file=f)
 
-def __write_cmake_toolchain_file(f: TextIO, toolchain) -> None:
+def __write_cmake_toolchain_file(f: TextIO, toolchain: AnyToolchain) -> None:
     if '-darwin' in toolchain.actual_arch:
         cmake_system_name = 'Darwin'
     elif toolchain.is_windows:
@@ -54,7 +55,7 @@ set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
 """)
 
-def configure(toolchain, src: str, build: str, args: list[str]=[], env: Optional[Mapping[str, str]]=None) -> None:
+def configure(toolchain: AnyToolchain, src: str, build: str, args: list[str]=[], env: Optional[Mapping[str, str]]=None) -> None:
     cross_args = []
 
     if toolchain.is_windows:
@@ -103,7 +104,7 @@ class CmakeProject(Project):
         self.windows_configure_args = windows_configure_args
         self.env = env
 
-    def configure(self, toolchain) -> str:
+    def configure(self, toolchain: AnyToolchain) -> str:
         src = self.unpack(toolchain)
         build = self.make_build_path(toolchain)
         configure_args = self.configure_args
@@ -112,7 +113,7 @@ class CmakeProject(Project):
         configure(toolchain, src, build, configure_args, self.env)
         return build
 
-    def _build(self, toolchain) -> None:
+    def _build(self, toolchain: AnyToolchain) -> None:
         build = self.configure(toolchain)
         subprocess.check_call(['ninja', '-v', 'install'],
                               cwd=build, env=toolchain.env)
diff --git a/python/build/makeproject.py b/python/build/makeproject.py
index c9a2b6eb9..d8d0910ac 100644
--- a/python/build/makeproject.py
+++ b/python/build/makeproject.py
@@ -2,6 +2,7 @@ import subprocess, multiprocessing
 from typing import Optional
 
 from build.project import Project
+from .toolchain import AnyToolchain
 
 class MakeProject(Project):
     def __init__(self, url: str, md5: str, installed: str,
@@ -18,17 +19,17 @@ class MakeProject(Project):
             # default to 12, if multiprocessing.cpu_count() is not implemented
             return 12
 
-    def get_make_args(self, toolchain) -> list[str]:
+    def get_make_args(self, toolchain: AnyToolchain) -> list[str]:
         return ['--quiet', '-j' + str(self.get_simultaneous_jobs())]
 
-    def get_make_install_args(self, toolchain) -> list[str]:
+    def get_make_install_args(self, toolchain: AnyToolchain) -> list[str]:
         return ['--quiet', self.install_target]
 
-    def make(self, toolchain, wd: str, args: list[str]) -> None:
+    def make(self, toolchain: AnyToolchain, wd: str, args: list[str]) -> None:
         subprocess.check_call(['make'] + args,
                               cwd=wd, env=toolchain.env)
 
-    def build_make(self, toolchain, wd: str, install: bool=True) -> None:
+    def build_make(self, toolchain: AnyToolchain, wd: str, install: bool=True) -> None:
         self.make(toolchain, wd, self.get_make_args(toolchain))
         if install:
             self.make(toolchain, wd, self.get_make_install_args(toolchain))
diff --git a/python/build/meson.py b/python/build/meson.py
index e585800f1..ffcb5d38a 100644
--- a/python/build/meson.py
+++ b/python/build/meson.py
@@ -4,8 +4,9 @@ import platform
 from typing import Optional
 
 from build.project import Project
+from .toolchain import AnyToolchain
 
-def make_cross_file(toolchain) -> str:
+def make_cross_file(toolchain: AnyToolchain) -> str:
     if toolchain.is_windows:
         system = 'windows'
         windres = "windres = '%s'" % toolchain.windres
@@ -81,7 +82,7 @@ endian = '{endian}'
 """)
     return path
 
-def configure(toolchain, src: str, build: str, args: list[str]=[]) -> None:
+def configure(toolchain: AnyToolchain, src: str, build: str, args: list[str]=[]) -> None:
     cross_file = make_cross_file(toolchain)
     configure = [
         'meson', 'setup',
@@ -110,13 +111,13 @@ class MesonProject(Project):
         Project.__init__(self, url, md5, installed, **kwargs)
         self.configure_args = configure_args
 
-    def configure(self, toolchain) -> str:
+    def configure(self, toolchain: AnyToolchain) -> str:
         src = self.unpack(toolchain)
         build = self.make_build_path(toolchain)
         configure(toolchain, src, build, self.configure_args)
         return build
 
-    def _build(self, toolchain) -> None:
+    def _build(self, toolchain: AnyToolchain) -> None:
         build = self.configure(toolchain)
         subprocess.check_call(['ninja', '-v', 'install'],
                               cwd=build, env=toolchain.env)
diff --git a/python/build/openssl.py b/python/build/openssl.py
index 053fe97b8..df63f2738 100644
--- a/python/build/openssl.py
+++ b/python/build/openssl.py
@@ -2,13 +2,14 @@ import subprocess
 from typing import Optional
 
 from build.makeproject import MakeProject
+from .toolchain import AnyToolchain
 
 class OpenSSLProject(MakeProject):
     def __init__(self, url: str, md5: str, installed: str,
                  **kwargs):
         MakeProject.__init__(self, url, md5, installed, install_target='install_dev', **kwargs)
 
-    def get_make_args(self, toolchain) -> list[str]:
+    def get_make_args(self, toolchain: AnyToolchain) -> list[str]:
         return MakeProject.get_make_args(self, toolchain) + [
             'CC=' + toolchain.cc,
             'CFLAGS=' + toolchain.cflags,
@@ -18,13 +19,13 @@ class OpenSSLProject(MakeProject):
             'build_libs',
         ]
 
-    def get_make_install_args(self, toolchain) -> list[str]:
+    def get_make_install_args(self, toolchain: AnyToolchain) -> list[str]:
         # OpenSSL's Makefile runs "ranlib" during installation
         return MakeProject.get_make_install_args(self, toolchain) + [
             'RANLIB=' + toolchain.ranlib,
         ]
 
-    def _build(self, toolchain) -> None:
+    def _build(self, toolchain: AnyToolchain) -> None:
         src = self.unpack(toolchain, out_of_tree=False)
 
         # OpenSSL has a weird target architecture scheme with lots of
diff --git a/python/build/project.py b/python/build/project.py
index 3607d4942..12791a05a 100644
--- a/python/build/project.py
+++ b/python/build/project.py
@@ -5,6 +5,7 @@ from typing import cast, BinaryIO, Optional
 from build.download import download_and_verify
 from build.tar import untar
 from build.quilt import push_all
+from .toolchain import AnyToolchain
 
 class Project:
     def __init__(self, url: str, md5: str, installed: str,
@@ -41,10 +42,10 @@ class Project:
         self.edits = edits
         self.use_cxx = use_cxx
 
-    def download(self, toolchain) -> str:
+    def download(self, toolchain: AnyToolchain) -> str:
         return download_and_verify(self.url, self.md5, toolchain.tarball_path)
 
-    def is_installed(self, toolchain) -> bool:
+    def is_installed(self, toolchain: AnyToolchain) -> bool:
         tarball = self.download(toolchain)
         installed = os.path.join(toolchain.install_prefix, self.installed)
         tarball_mtime = os.path.getmtime(tarball)
@@ -53,7 +54,7 @@ class Project:
         except FileNotFoundError:
             return False
 
-    def unpack(self, toolchain, out_of_tree: bool=True) -> str:
+    def unpack(self, toolchain: AnyToolchain, out_of_tree: bool=True) -> str:
         if out_of_tree:
             parent_path = toolchain.src_path
         else:
@@ -74,7 +75,7 @@ class Project:
 
         return path
 
-    def make_build_path(self, toolchain, lazy: bool=False) -> str:
+    def make_build_path(self, toolchain: AnyToolchain, lazy: bool=False) -> str:
         path = os.path.join(toolchain.build_path, self.base)
         if lazy and os.path.isdir(path):
             return path
@@ -85,5 +86,5 @@ class Project:
         os.makedirs(path, exist_ok=True)
         return path
 
-    def build(self, toolchain) -> None:
+    def build(self, toolchain: AnyToolchain) -> None:
         self._build(toolchain)
diff --git a/python/build/quilt.py b/python/build/quilt.py
index 8751404db..03adf0e42 100644
--- a/python/build/quilt.py
+++ b/python/build/quilt.py
@@ -1,10 +1,12 @@
 import subprocess
 from typing import Union
 
-def run_quilt(toolchain, cwd: str, patches_path: str, *args: str) -> None:
+from .toolchain import AnyToolchain
+
+def run_quilt(toolchain: AnyToolchain, cwd: str, patches_path: str, *args: str) -> None:
     env = dict(toolchain.env)
     env['QUILT_PATCHES'] = patches_path
     subprocess.check_call(['quilt'] + list(args), cwd=cwd, env=env)
 
-def push_all(toolchain, src_path: str, patches_path: str) -> None:
+def push_all(toolchain: AnyToolchain, src_path: str, patches_path: str) -> None:
     run_quilt(toolchain, src_path, patches_path, 'push', '-a')
diff --git a/python/build/toolchain.py b/python/build/toolchain.py
index 78d4954c7..15a29ca20 100644
--- a/python/build/toolchain.py
+++ b/python/build/toolchain.py
@@ -1,5 +1,6 @@
 import os.path
 import shutil
+from typing import Union
 
 android_abis = {
     'armeabi-v7a': {
@@ -172,3 +173,5 @@ class MingwToolchain:
         self.pkg_config = shutil.copy(os.path.join(top_path, 'build', 'pkg-config.sh'),
                                       os.path.join(bin_dir, 'pkg-config'))
         self.env['PKG_CONFIG'] = self.pkg_config
+
+AnyToolchain = Union[AndroidNdkToolchain, MingwToolchain]
diff --git a/python/build/zlib.py b/python/build/zlib.py
index 98eede580..2007c6c6d 100644
--- a/python/build/zlib.py
+++ b/python/build/zlib.py
@@ -2,13 +2,14 @@ import subprocess
 from typing import Optional
 
 from build.makeproject import MakeProject
+from .toolchain import AnyToolchain
 
 class ZlibProject(MakeProject):
     def __init__(self, url: str, md5: str, installed: str,
                  **kwargs):
         MakeProject.__init__(self, url, md5, installed, **kwargs)
 
-    def get_make_args(self, toolchain) -> list[str]:
+    def get_make_args(self, toolchain: AnyToolchain) -> list[str]:
         return MakeProject.get_make_args(self, toolchain) + [
             'CC=' + toolchain.cc + ' ' + toolchain.cppflags + ' ' + toolchain.cflags,
             'CPP=' + toolchain.cc + ' -E ' + toolchain.cppflags,
@@ -19,13 +20,13 @@ class ZlibProject(MakeProject):
             'libz.a'
         ]
 
-    def get_make_install_args(self, toolchain) -> list[str]:
+    def get_make_install_args(self, toolchain: AnyToolchain) -> list[str]:
         return [
             'RANLIB=' + toolchain.ranlib,
             self.install_target
         ]
 
-    def _build(self, toolchain) -> None:
+    def _build(self, toolchain: AnyToolchain) -> None:
         src = self.unpack(toolchain, out_of_tree=False)
 
         subprocess.check_call(['./configure', '--prefix=' + toolchain.install_prefix, '--static'],