diff --git a/Lib/mimetypes.py b/Lib/mimetypes.py
index d7c4e8444f8dec..2a61249a46a366 100644
--- a/Lib/mimetypes.py
+++ b/Lib/mimetypes.py
@@ -15,6 +15,7 @@
 suffix_map -- dictionary mapping suffixes to suffixes
 encodings_map -- dictionary mapping suffixes to encodings
 types_map -- dictionary mapping suffixes to types
+duplicate_types_map -- dictionary mapping suffixes to types for suffixes that map to multiple types
 
 Functions:
 
@@ -42,7 +43,8 @@
     "knownfiles", "inited", "MimeTypes",
     "guess_type", "guess_file_type", "guess_all_extensions", "guess_extension",
     "add_type", "init", "read_mime_types",
-    "suffix_map", "encodings_map", "types_map", "common_types"
+    "suffix_map", "encodings_map", "types_map", "common_types",
+    "duplicate_ext_types",
 ]
 
 knownfiles = [
@@ -80,6 +82,11 @@ def __init__(self, filenames=(), strict=True):
             self.add_type(type, ext, True)
         for (ext, type) in _common_types_default.items():
             self.add_type(type, ext, False)
+        for (ext, type) in _duplicate_ext_types_default.items():
+            exts = self.types_map_inv[strict].setdefault(type, [])
+            if ext not in exts:
+                exts.append(ext)
+
         for name in filenames:
             self.read(name, strict)
 
@@ -425,6 +432,7 @@ def _default_mime_types():
     global suffix_map, _suffix_map_default
     global encodings_map, _encodings_map_default
     global types_map, _types_map_default
+    global duplicate_ext_types, _duplicate_ext_types_default
     global common_types, _common_types_default
 
     suffix_map = _suffix_map_default = {
@@ -608,6 +616,20 @@ def _default_mime_types():
         '.movie'  : 'video/x-sgi-movie',
         }
 
+    # Some extensions in the default list are linked to multiple mimetypes.
+    # If you need to add a type that duplicates an extension in the default
+    # map, add it here.
+
+    # Please sort these too.
+    # Make sure the entry with the preferred file extension for a particular mime type
+    # appears before any others of the same mimetype.
+    duplicate_ext_types = _duplicate_ext_types_default = {
+        '.3gp'   : 'video/3gpp',
+        '.3gpp'  : 'video/3gpp',
+        '.3g2'   : 'video/3gpp2',
+        '.3gpp2' : 'video/3gpp2',
+    }
+
     # These are non-standard types, commonly found in the wild.  They will
     # only match if strict=0 flag is given to the API methods.
 
diff --git a/Lib/test/test_mimetypes.py b/Lib/test/test_mimetypes.py
index 58f6a4dfae08ba..ca63edc42a710f 100644
--- a/Lib/test/test_mimetypes.py
+++ b/Lib/test/test_mimetypes.py
@@ -107,6 +107,13 @@ def test_read_mime_types(self):
             mock_open.assert_called_with(filename, encoding='utf-8')
         eq(mime_dict[".Français"], "application/no-mans-land")
 
+    def test_duplicate_ext_types(self):
+        # assert that each extension in the duplicate map is also in the default map
+        # for a different type
+        for ext, type in mimetypes.duplicate_ext_types.items():
+            self.assertIn(ext, mimetypes._types_map_default)
+            self.assertNotEqual(type, mimetypes._types_map_default[ext])
+
     def test_non_standard_types(self):
         eq = self.assertEqual
         # First try strict
@@ -231,6 +238,8 @@ def check_extensions():
             self.assertEqual(mimetypes.guess_extension('application/x-texinfo'), '.texi')
             self.assertEqual(mimetypes.guess_extension('application/x-troff'), '.roff')
             self.assertEqual(mimetypes.guess_extension('application/xml'), '.xsl')
+            self.assertEqual(mimetypes.guess_extension('audio/3gpp'), '.3gp')
+            self.assertEqual(mimetypes.guess_extension('audio/3gpp2'), '.3g2')
             self.assertEqual(mimetypes.guess_extension('audio/mpeg'), '.mp3')
             self.assertEqual(mimetypes.guess_extension('image/avif'), '.avif')
             self.assertEqual(mimetypes.guess_extension('image/webp'), '.webp')
@@ -241,6 +250,8 @@ def check_extensions():
             self.assertEqual(mimetypes.guess_extension('text/plain'), '.txt')
             self.assertEqual(mimetypes.guess_extension('text/rtf'), '.rtf')
             self.assertEqual(mimetypes.guess_extension('text/x-rst'), '.rst')
+            self.assertEqual(mimetypes.guess_extension('video/3gpp'), '.3gp')
+            self.assertEqual(mimetypes.guess_extension('video/3gpp2'), '.3g2')
             self.assertEqual(mimetypes.guess_extension('video/mpeg'), '.mpeg')
             self.assertEqual(mimetypes.guess_extension('video/quicktime'), '.mov')
 
@@ -255,6 +266,7 @@ def test_init_stability(self):
         encodings_map = mimetypes.encodings_map
         types_map = mimetypes.types_map
         common_types = mimetypes.common_types
+        duplicate_ext_types = mimetypes.duplicate_ext_types
 
         mimetypes.init()
         self.assertIsNot(suffix_map, mimetypes.suffix_map)
@@ -265,6 +277,7 @@ def test_init_stability(self):
         self.assertEqual(encodings_map, mimetypes.encodings_map)
         self.assertEqual(types_map, mimetypes.types_map)
         self.assertEqual(common_types, mimetypes.common_types)
+        self.assertEqual(duplicate_ext_types, mimetypes.duplicate_ext_types)
 
     def test_path_like_ob(self):
         filename = "LICENSE.txt"
diff --git a/Misc/NEWS.d/next/Library/2024-08-02-20-02-38.gh-issue-122631.p4QdB2.rst b/Misc/NEWS.d/next/Library/2024-08-02-20-02-38.gh-issue-122631.p4QdB2.rst
new file mode 100644
index 00000000000000..a2fe1c298187bb
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-08-02-20-02-38.gh-issue-122631.p4QdB2.rst
@@ -0,0 +1,4 @@
+Add :mod:`mimetypes` support for `video/3gpp`_ and `video/3gpp2`_.
+
+.. _video/3gpp: https://www.iana.org/assignments/media-types/video/3gpp
+.. _video/3gpp2: https://www.iana.org/assignments/media-types/video/3gpp2