diff --git a/CHANGES.rst b/CHANGES.rst
index 50a81aaf3..937d2d0fa 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -22,7 +22,10 @@ This list is detailed and covers changes in each pre-release version.
 Unreleased
 ----------
 
-Nothing yet.
+- Changed an internal detail of how tomli is imported, so that tomli can use
+  coverage.py for their own test suite (`issue 1228`_).
+
+.. _issue 1228: https://github.com/nedbat/coveragepy/issues/1228
 
 
 .. _changes_60:
diff --git a/coverage/misc.py b/coverage/misc.py
index 11dad23e0..cd4a77401 100644
--- a/coverage/misc.py
+++ b/coverage/misc.py
@@ -5,6 +5,7 @@
 
 import errno
 import hashlib
+import importlib
 import importlib.util
 import inspect
 import locale
@@ -43,6 +44,32 @@ def isolate_module(mod):
 os = isolate_module(os)
 
 
+def import_third_party(modname):
+    """Import a third-party module we need, but might not be installed.
+
+    This also cleans out the module after the import, so that coverage won't
+    appear to have imported it.  This lets the third party use coverage for
+    their own tests.
+
+    Arguments:
+        modname (str): the name of the module to import.
+
+    Returns:
+        The imported module, or None if the module couldn't be imported.
+
+    """
+    try:
+        mod = importlib.import_module(modname)
+    except ImportError:
+        mod = None
+
+    imported = [m for m in sys.modules if m.startswith(modname)]
+    for name in imported:
+        del sys.modules[name]
+
+    return mod
+
+
 def dummy_decorator_with_args(*args_unused, **kwargs_unused):
     """Dummy no-op implementation of a decorator with arguments."""
     def _decorator(func):
diff --git a/coverage/tomlconfig.py b/coverage/tomlconfig.py
index 203192c93..3301acc8e 100644
--- a/coverage/tomlconfig.py
+++ b/coverage/tomlconfig.py
@@ -8,13 +8,10 @@
 import re
 
 from coverage.exceptions import CoverageException
-from coverage.misc import substitute_variables
+from coverage.misc import import_third_party, substitute_variables
 
 # TOML support is an install-time extra option.
-try:
-    import tomli
-except ImportError:         # pragma: not covered
-    tomli = None
+tomli = import_third_party("tomli")
 
 
 class TomlDecodeError(Exception):
diff --git a/tests/test_misc.py b/tests/test_misc.py
index 3858c4f8b..077c24344 100644
--- a/tests/test_misc.py
+++ b/tests/test_misc.py
@@ -3,11 +3,13 @@
 
 """Tests of miscellaneous stuff."""
 
+import sys
+
 import pytest
 
 from coverage.exceptions import CoverageException
 from coverage.misc import contract, dummy_decorator_with_args, file_be_gone
-from coverage.misc import Hasher, one_of, substitute_variables
+from coverage.misc import Hasher, one_of, substitute_variables, import_third_party
 from coverage.misc import USE_CONTRACTS
 
 from tests.coveragetest import CoverageTest
@@ -155,3 +157,19 @@ def test_substitute_variables_errors(text):
         substitute_variables(text, VARS)
     assert text in str(exc_info.value)
     assert "Variable NOTHING is undefined" in str(exc_info.value)
+
+
+class ImportThirdPartyTest(CoverageTest):
+    """Test import_third_party."""
+
+    run_in_temp_dir = False
+
+    def test_success(self):
+        mod = import_third_party("pytest")
+        assert mod.__name__ == "pytest"
+        assert "pytest" not in sys.modules
+
+    def test_failure(self):
+        mod = import_third_party("xyzzy")
+        assert mod is None
+        assert "xyzzy" not in sys.modules