diff --git a/Lib/test/test_utf8_mode.py b/Lib/test/test_utf8_mode.py
index 554abfab3163159..06fe1979ddcc705 100644
--- a/Lib/test/test_utf8_mode.py
+++ b/Lib/test/test_utf8_mode.py
@@ -228,6 +228,8 @@ def check(utf8_opt, expected, **kw):
 
         if sys.platform == 'darwin' or support.is_android:
             c_arg = arg_utf8
+        elif sys.platform.startswith("aix"):
+            c_arg = arg.decode('iso-8859-1')
         else:
             c_arg = arg_ascii
         for loc in POSIX_LOCALES:
diff --git a/Misc/NEWS.d/next/Tests/2018-08-25-13-28-18.bpo-34347.IsRDPB.rst b/Misc/NEWS.d/next/Tests/2018-08-25-13-28-18.bpo-34347.IsRDPB.rst
new file mode 100644
index 000000000000000..e581f605f75a208
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2018-08-25-13-28-18.bpo-34347.IsRDPB.rst
@@ -0,0 +1 @@
+Fix ``test_utf8_mode.test_cmd_line`` for AIX.  Patch by M. Felt