diff --git a/.travis.yml b/.travis.yml
index 25e60c2..191be87 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -33,7 +33,8 @@ matrix:
         - pip install .[testing]
       script:
         - pytest --cov-report term-missing
-        - mypy .
+        # In recent versions of setuptools, pip install . creates a "build" directory
+        - mypy . --exclude=build
     - stage: build
       python: '3.8'
       install:
@@ -41,7 +42,8 @@ matrix:
         - pip install .[testing]
       script:
         - pytest --cov-report term-missing
-        - mypy .
+        # In recent versions of setuptools, pip install . creates a "build" directory
+        - mypy . --exclude=build
     - stage: deploy
       if: tag =~ ^[0-9]+\.[0-9]+\.[0-9]+
       python: '3.6'
diff --git a/setup.py b/setup.py
index de680ec..c7370b9 100755
--- a/setup.py
+++ b/setup.py
@@ -22,7 +22,7 @@ def readme():
 
 
 install_requires = [
-    'attrs>=17.4,<20',
+    'attrs>=17.4,<22',
     'conformity>=1.26.9,!=1.27.0,<2.0',
     'enum34;python_version<"3.4"',
     'six',
@@ -43,6 +43,7 @@ def readme():
     'pytest-runner',
     'mock',
     'more-itertools~=5.0',  # We must pin this, because 6.0 requires Python 3.
+    'importlib-metadata',  # We need to explicitly install it to avoid incompatibilities with setuptools
 ] + mypy_require
 
 
diff --git a/tests/unit/recorders/test_default.py b/tests/unit/recorders/test_default.py
index 13f84db..189486c 100644
--- a/tests/unit/recorders/test_default.py
+++ b/tests/unit/recorders/test_default.py
@@ -3,6 +3,7 @@
     unicode_literals,
 )
 
+import datetime
 import time
 from typing import (
     Any,
@@ -578,11 +579,11 @@ def se():
             mock_publish.reset_mock()
 
             recorder.unpublished_metrics_count = 1
-            frozen_time.tick(9)
+            frozen_time.tick(datetime.timedelta(seconds=9))
             recorder.publish_if_full_or_old()
             assert mock_publish.call_count == 0
 
-            frozen_time.tick(1)
+            frozen_time.tick(datetime.timedelta(seconds=1))
             recorder.publish_if_full_or_old()
             mock_publish.assert_called_once_with()
             mock_publish.reset_mock()
@@ -591,11 +592,11 @@ def se():
             recorder.publish_if_full_or_old()
             assert mock_publish.call_count == 0
 
-            frozen_time.tick(13)
+            frozen_time.tick(datetime.timedelta(seconds=13))
             recorder.publish_if_full_or_old(max_age=14)
             assert mock_publish.call_count == 0
 
-            frozen_time.tick(1)
+            frozen_time.tick(datetime.timedelta(seconds=1))
             recorder.publish_if_full_or_old()
             mock_publish.assert_called_once_with()
             mock_publish.reset_mock()
@@ -620,11 +621,11 @@ def se():
             recorder.throttled_publish_all()
             assert mock_publish.call_count == 0
 
-            frozen_time.tick(9)
+            frozen_time.tick(datetime.timedelta(seconds=9))
             recorder.throttled_publish_all()
             assert mock_publish.call_count == 0
 
-            frozen_time.tick(1)
+            frozen_time.tick(datetime.timedelta(seconds=1))
             recorder.throttled_publish_all()
             mock_publish.assert_called_once_with()
             mock_publish.reset_mock()
@@ -633,11 +634,11 @@ def se():
             recorder.throttled_publish_all()
             assert mock_publish.call_count == 0
 
-            frozen_time.tick(13)
+            frozen_time.tick(datetime.timedelta(seconds=13))
             recorder.throttled_publish_all(14)
             assert mock_publish.call_count == 0
 
-            frozen_time.tick(1)
+            frozen_time.tick(datetime.timedelta(seconds=1))
             recorder.throttled_publish_all()
             mock_publish.assert_called_once_with()
             mock_publish.reset_mock()