# Link against shared blake3 library. Gentoo bug 943281.
# Set FORCE_SYSTEM_BLAKE3=1 to force use of installed system library.

diff --git a/c_impl/setup.py b/c_impl/setup.py
index 417385b..2a664f0 100644
--- a/c_impl/setup.py
+++ b/c_impl/setup.py
@@ -69,6 +69,9 @@ def is_aarch64():
 def force_intrinsics():
     return os.environ.get("FORCE_INTRINSICS") == "1"
 
+def force_system_blake3():
+    # force use of system library for blake3
+    return os.environ.get("FORCE_SYSTEM_BLAKE3") == "1"
 
 def compile_x86_intrinsics():
     object_files = []
@@ -203,9 +206,17 @@ def prepare_extension():
         "vendor/blake3_dispatch.c",
         "vendor/blake3_portable.c",
     ]
+    include_dirs=[
+        "vendor",
+    ],
+    extra_link_args = [ "-lblake3" ]
     target = platform.machine()
     extra_objects = []
-    if is_macos():
+    if force_system_blake3():
+        print("using installed system library")
+        sources = sources[:1]
+        include_dirs = []
+    elif is_macos():
         # On macOS we build a "universal" binary containing both x86 and ARM
         # code.
         extra_objects = compile_macos_universal_staticlib()
@@ -239,10 +250,9 @@ def prepare_extension():
     return setuptools.Extension(
         "blake3",
         sources=sources,
-        include_dirs=[
-            "vendor",
-        ],
+        include_dirs=include_dirs,
         extra_objects=extra_objects,
+        extra_link_args=extra_link_args,
         define_macros=[
             ("SETUP_PY_VERSION", escape_preprocessor_string(VERSION)),
             ("SETUP_PY_DESCRIPTION", escape_preprocessor_string(DESCRIPTION)),