diff --git a/Lib/packaging/command/build_ext.py b/Lib/packaging/command/build_ext.py
index 4f375b6..4c85822 100644
--- a/Lib/packaging/command/build_ext.py
+++ b/Lib/packaging/command/build_ext.py
@@ -159,8 +159,7 @@
         if plat_py_include != py_include:
             self.include_dirs.append(plat_py_include)
 
-        if isinstance(self.libraries, str):
-            self.libraries = [self.libraries]
+        self.ensure_string_list('libraries')
 
         # Life is easier if we're not forever checking for None, so
         # simplify these options to empty lists if unset
diff --git a/Lib/packaging/tests/test_command_build_ext.py b/Lib/packaging/tests/test_command_build_ext.py
index 4883f38..161b000 100644
--- a/Lib/packaging/tests/test_command_build_ext.py
+++ b/Lib/packaging/tests/test_command_build_ext.py
@@ -141,21 +141,21 @@
         # make sure cmd.libraries is turned into a list
         # if it's a string
         cmd = build_ext(dist)
-        cmd.libraries = 'my_lib'
+        cmd.libraries = 'my_lib, other_lib lastlib'
         cmd.finalize_options()
-        self.assertEqual(cmd.libraries, ['my_lib'])
+        self.assertEqual(cmd.libraries, ['my_lib', 'other_lib', 'lastlib'])
 
         # make sure cmd.library_dirs is turned into a list
         # if it's a string
         cmd = build_ext(dist)
-        cmd.library_dirs = 'my_lib_dir'
+        cmd.library_dirs = 'my_lib_dir%sother_lib_dir' % os.pathsep
         cmd.finalize_options()
-        self.assertIn('my_lib_dir', cmd.library_dirs)
+        self.assertEqual(cmd.library_dirs, ['my_lib_dir', 'other_lib_dir'])
 
         # make sure rpath is turned into a list
-        # if it's a list of os.pathsep's paths
+        # if it's a string
         cmd = build_ext(dist)
-        cmd.rpath = os.pathsep.join(['one', 'two'])
+        cmd.rpath = 'one%stwo' % os.pathsep
         cmd.finalize_options()
         self.assertEqual(cmd.rpath, ['one', 'two'])
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 1e67160..faef50a 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -472,8 +472,9 @@
 - Issue #13015: Fix a possible reference leak in defaultdict.__repr__.
   Patch by Suman Saha.
 
-- Issue #1326113: distutils' build_ext command --libraries option now
-  correctly parses multiple values separated by whitespace or commas.
+- Issue #1326113: distutils' and packaging's build_ext commands option now
+  correctly parses multiple values (separated by whitespace or commas) given
+  to their --libraries option.
 
 - Issue #10287: nntplib now queries the server's CAPABILITIES first before
   sending MODE READER, and only sends it if not already in READER mode.