--- a/build_config.py	2026-06-18 23:31:55.516921459 +0800
+++ b/build_config.py	2026-06-18 23:36:19.840047830 +0800
@@ -1,4 +1,5 @@
 import shutil
+import subprocess
 import tarfile
 from abc import ABC, abstractmethod
 from enum import Enum
@@ -253,7 +254,7 @@
     # TODO: Since the C routines used when no-asm is passed are ostensibly less efficient than the corresponding
     # assembly routines, we could consider only passing `no-asm` when we're building for the macOS M* target.
     _OPENSSL_CONF_CMD = (
-        "perl Configure {target} zlib no-zlib-dynamic no-shared enable-rc5 enable-md2 enable-gost "
+        "perl Configure {target} zlib no-shared enable-rc5 enable-md2 enable-gost "
         "enable-cast enable-idea enable-ripemd enable-mdc2 no-asm --with-zlib-include={zlib_include_path} "
         "--with-zlib-lib={zlib_lib_path} {extra_args}"
     )
@@ -312,7 +313,7 @@
         return "OpenSSL_1_1_1w"
 
     _OPENSSL_CONF_CMD = (
-        "perl Configure {target} zlib no-zlib-dynamic no-shared enable-rc5 enable-md2 enable-gost "
+        "perl Configure {target} zlib no-shared enable-rc5 enable-md2 enable-gost "
         "enable-cast enable-idea enable-ripemd enable-mdc2 --with-zlib-include={zlib_include_path} "
         "--with-zlib-lib={zlib_lib_path} enable-weak-ssl-ciphers enable-tls1_3 {extra_args} no-async"
     )
@@ -362,54 +363,29 @@
             return self.src_path / "apps" / "openssl"
 
 
+def _pkg_config(arg: str, package: str) -> str:
+    return subprocess.check_output(["pkg-config", arg, package], text=True).strip()
+
+
 class ZlibBuildConfig(BuildConfig):
-    @property
-    def src_tar_gz_url(self) -> str:
-        return "https://www.zlib.net/fossils/zlib-1.2.13.tar.gz"
+    """Use the system-provided shared zlib; OpenSSL is configured for dynamic (dlopen) mode."""
 
     @property
     def src_path(self) -> Path:
-        return _DEPS_PATH / "zlib-1.2.13"
-
-    def build(self, ctx: "Context") -> None:
-        if self.platform in [
-            SupportedPlatformEnum.WINDOWS_32,
-            SupportedPlatformEnum.WINDOWS_64,
-        ]:
-            if self.platform == SupportedPlatformEnum.WINDOWS_32:
-                build_platform = "Win32"
-            else:
-                build_platform = "x64"
+        return Path(_pkg_config("--variable=includedir", "zlib"))
 
-            # Assuming default path for Visual Studio 2022
-            msbuild_path = Path(
-                "C:\\Program Files\\Microsoft Visual Studio\\2022\\Enterprise\\MSBuild\\Current\\Bin\\MSBuild.exe"
-            )
-            assert msbuild_path.exists()
-
-            vs_contrib_path = self.src_path / "contrib" / "vstudio"
-            with ctx.cd(str(vs_contrib_path)):
-                ctx.run(f'"{msbuild_path}" vc14\\zlibvc.sln /P:Configuration=Release /P:Platform={build_platform}')
+    @property
+    def src_tar_gz_url(self) -> str:
+        return ""
 
-        else:
-            # Linux/macOS build
-            with ctx.cd(str(self.src_path)):
-                ctx.run('CFLAGS="-fPIC" ./configure -static')
-                ctx.run("make clean")
-                ctx.run("make")
+    def build(self, ctx: "Context") -> None:
+        pass  # system zlib requires no build step
 
     @property
     def libz_path(self) -> Path:
-        if self.platform in [
-            SupportedPlatformEnum.WINDOWS_32,
-            SupportedPlatformEnum.WINDOWS_64,
-        ]:
-            arch = "x86" if self.platform == SupportedPlatformEnum.WINDOWS_32 else "x64"
-            zlib_lib_path = self.src_path / "contrib" / "vstudio" / "vc14" / arch / "ZlibStatRelease" / "zlibstat.lib"
-        else:
-            zlib_lib_path = self.src_path / "libz.a"
-        return zlib_lib_path
+        lib_dir = Path(_pkg_config("--variable=libdir", "zlib"))
+        return lib_dir / "libz.so"
 
     @property
     def include_path(self) -> Path:
-        return self.src_path
+        return Path(_pkg_config("--variable=includedir", "zlib"))
--- a/setup.py	2026-06-18 23:31:55.518111784 +0800
+++ b/setup.py	2026-06-19 00:20:14.453399562 +0800
@@ -4,7 +4,6 @@
 
 from build_config import (
     ModernOpenSslBuildConfig,
-    ZlibBuildConfig,
     LegacyOpenSslBuildConfig,
     SupportedPlatformEnum,
     CURRENT_PLATFORM,
@@ -104,8 +103,9 @@
         # https://github.com/nabla-c0d3/nassl/issues/28
         BASE_NASSL_EXT_SETUP["extra_link_args"].append("-Wl,-z,noexecstack")
 
-zlib_config = ZlibBuildConfig(CURRENT_PLATFORM)
-
+# Link against system zlib so inflateEnd/deflateEnd symbols from libcrypto.a are resolved at runtime
+if CURRENT_PLATFORM not in [SupportedPlatformEnum.WINDOWS_32, SupportedPlatformEnum.WINDOWS_64]:
+    BASE_NASSL_EXT_SETUP["extra_link_args"].append("-lz")
 
 # The configure the setup for legacy nassl
 legacy_openssl_config = LegacyOpenSslBuildConfig(CURRENT_PLATFORM)
@@ -120,7 +120,6 @@
             # The order matters on some flavors of Linux
             str(legacy_openssl_config.libssl_path),
             str(legacy_openssl_config.libcrypto_path),
-            str(zlib_config.libz_path),
         ],
     }
 )
@@ -137,7 +136,6 @@
             # The order matters on some flavors of Linux
             str(modern_openssl_config.libssl_path),
             str(modern_openssl_config.libcrypto_path),
-            str(zlib_config.libz_path),
         ],
     }
 )