diff --git a/doc/source/whatsnew/v1.2.1.rst b/doc/source/whatsnew/v1.2.1.rst
index 37562be17f02e..649b17e255f3d 100644
--- a/doc/source/whatsnew/v1.2.1.rst
+++ b/doc/source/whatsnew/v1.2.1.rst
@@ -41,7 +41,7 @@ I/O
 
 Other
 ~~~~~
--
+- Fixed build failure on MacOS 11 in Python 3.9.1 (:issue:`38766`)
 -
 
 .. ---------------------------------------------------------------------------
diff --git a/setup.py b/setup.py
index a25fe95e025b3..f9c4a1158fee0 100755
--- a/setup.py
+++ b/setup.py
@@ -435,7 +435,7 @@ def run(self):
             "MACOSX_DEPLOYMENT_TARGET", current_system
         )
         if (
-            LooseVersion(python_target) < "10.9"
+            LooseVersion(str(python_target)) < "10.9"
             and LooseVersion(current_system) >= "10.9"
         ):
             os.environ["MACOSX_DEPLOYMENT_TARGET"] = "10.9"