diff --git a/AUTHORS b/AUTHORS
index e11400c1f..def641c95 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -160,6 +160,7 @@ Manuel Krebber
 Marc Schlaich
 Marcelo Duarte Trevisani
 Marcin Bachry
+Marco Gorelli
 Mark Abramowitz
 Markus Unterwaditzer
 Martijn Faassen
diff --git a/changelog/5990.improvement.rst b/changelog/5990.improvement.rst
new file mode 100644
index 000000000..6f5ad648e
--- /dev/null
+++ b/changelog/5990.improvement.rst
@@ -0,0 +1 @@
+Fix plurality mismatch in test summary (e.g. display "1 error" instead of "1 errors").
diff --git a/src/_pytest/main.py b/src/_pytest/main.py
index ad65ed299..7b3855e6c 100644
--- a/src/_pytest/main.py
+++ b/src/_pytest/main.py
@@ -248,7 +248,10 @@ def pytest_collection(session):
 
 def pytest_runtestloop(session):
     if session.testsfailed and not session.config.option.continue_on_collection_errors:
-        raise session.Interrupted("%d errors during collection" % session.testsfailed)
+        raise session.Interrupted(
+            "%d error%s during collection"
+            % (session.testsfailed, "s" if session.testsfailed != 1 else "")
+        )
 
     if session.config.option.collectonly:
         return True
diff --git a/src/_pytest/terminal.py b/src/_pytest/terminal.py
index 35f6d324b..228fc4219 100644
--- a/src/_pytest/terminal.py
+++ b/src/_pytest/terminal.py
@@ -539,7 +539,7 @@ class TerminalReporter:
             str(self._numcollected) + " item" + ("" if self._numcollected == 1 else "s")
         )
         if errors:
-            line += " / %d errors" % errors
+            line += " / %d error%s" % (errors, "s" if errors != 1 else "")
         if deselected:
             line += " / %d deselected" % deselected
         if skipped:
@@ -1056,6 +1056,19 @@ _color_for_type = {
 _color_for_type_default = "yellow"
 
 
+def _make_plural(count, noun):
+    # No need to pluralize words such as `failed` or `passed`.
+    if noun not in ["error", "warnings"]:
+        return count, noun
+
+    # The `warnings` key is plural. To avoid API breakage, we keep it that way but
+    # set it to singular here so we can determine plurality in the same way as we do
+    # for `error`.
+    noun = noun.replace("warnings", "warning")
+
+    return count, noun + "s" if count != 1 else noun
+
+
 def build_summary_stats_line(stats):
     known_types = (
         "failed passed skipped deselected xfailed xpassed warnings error".split()
@@ -1086,7 +1099,7 @@ def build_summary_stats_line(stats):
             )
             color = _color_for_type.get(key, _color_for_type_default)
             markup = {color: True, "bold": color == main_color}
-            parts.append(("%d %s" % (count, key), markup))
+            parts.append(("%d %s" % _make_plural(count, key), markup))
 
     if not parts:
         parts = [("no tests ran", {_color_for_type_default: True})]
diff --git a/testing/acceptance_test.py b/testing/acceptance_test.py
index 2bf56cb80..82c727fc6 100644
--- a/testing/acceptance_test.py
+++ b/testing/acceptance_test.py
@@ -628,7 +628,7 @@ class TestInvocationVariants:
         result = testdir.runpytest("--pyargs", "tpkg.test_hello", syspathinsert=True)
         assert result.ret != 0
 
-        result.stdout.fnmatch_lines(["collected*0*items*/*1*errors"])
+        result.stdout.fnmatch_lines(["collected*0*items*/*1*error"])
 
     def test_pyargs_only_imported_once(self, testdir):
         pkg = testdir.mkpydir("foo")
@@ -956,7 +956,7 @@ class TestDurations:
         testdir.makepyfile(test_collecterror="""xyz""")
         result = testdir.runpytest("--durations=2", "-k test_1")
         assert result.ret == 2
-        result.stdout.fnmatch_lines(["*Interrupted: 1 errors during collection*"])
+        result.stdout.fnmatch_lines(["*Interrupted: 1 error during collection*"])
         # Collection errors abort test execution, therefore no duration is
         # output
         result.stdout.no_fnmatch_line("*duration*")
diff --git a/testing/python/collect.py b/testing/python/collect.py
index 537047119..30f9841b5 100644
--- a/testing/python/collect.py
+++ b/testing/python/collect.py
@@ -1167,7 +1167,7 @@ def test_dont_collect_non_function_callable(testdir):
         [
             "*collected 1 item*",
             "*test_dont_collect_non_function_callable.py:2: *cannot collect 'test_a' because it is not a function*",
-            "*1 passed, 1 warnings in *",
+            "*1 passed, 1 warning in *",
         ]
     )
 
diff --git a/testing/python/fixtures.py b/testing/python/fixtures.py
index 6399863c7..6dca793e0 100644
--- a/testing/python/fixtures.py
+++ b/testing/python/fixtures.py
@@ -3081,7 +3081,7 @@ class TestErrors:
             *KeyError*
             *ERROR*teardown*test_2*
             *KeyError*
-            *3 pass*2 error*
+            *3 pass*2 errors*
         """
         )
 
diff --git a/testing/test_assertrewrite.py b/testing/test_assertrewrite.py
index 6c5de5c03..3aab3ac2a 100644
--- a/testing/test_assertrewrite.py
+++ b/testing/test_assertrewrite.py
@@ -122,7 +122,7 @@ class TestAssertionRewrite:
         }
         testdir.makepyfile(**contents)
         result = testdir.runpytest_subprocess()
-        assert "warnings" not in "".join(result.outlines)
+        assert "warning" not in "".join(result.outlines)
 
     def test_rewrites_plugin_as_a_package(self, testdir):
         pkgdir = testdir.mkpydir("plugin")
diff --git a/testing/test_capture.py b/testing/test_capture.py
index 4320a7cae..67aa0c77e 100644
--- a/testing/test_capture.py
+++ b/testing/test_capture.py
@@ -453,7 +453,7 @@ class TestCaptureFixture:
                 "E*capfd*capsys*same*time*",
                 "*ERROR*setup*test_two*",
                 "E*capsys*capfd*same*time*",
-                "*2 error*",
+                "*2 errors*",
             ]
         )
 
diff --git a/testing/test_collection.py b/testing/test_collection.py
index 7a5cf795b..259868357 100644
--- a/testing/test_collection.py
+++ b/testing/test_collection.py
@@ -892,7 +892,7 @@ def test_continue_on_collection_errors(testdir):
     assert res.ret == 1
 
     res.stdout.fnmatch_lines(
-        ["collected 2 items / 2 errors", "*1 failed, 1 passed, 2 error*"]
+        ["collected 2 items / 2 errors", "*1 failed, 1 passed, 2 errors*"]
     )
 
 
@@ -909,7 +909,7 @@ def test_continue_on_collection_errors_maxfail(testdir):
     res = testdir.runpytest("--continue-on-collection-errors", "--maxfail=3")
     assert res.ret == 1
 
-    res.stdout.fnmatch_lines(["collected 2 items / 2 errors", "*1 failed, 2 error*"])
+    res.stdout.fnmatch_lines(["collected 2 items / 2 errors", "*1 failed, 2 errors*"])
 
 
 def test_fixture_scope_sibling_conftests(testdir):
@@ -1253,7 +1253,7 @@ def test_collector_respects_tbstyle(testdir):
             '  File "*/test_collector_respects_tbstyle.py", line 1, in <module>',
             "    assert 0",
             "AssertionError: assert 0",
-            "*! Interrupted: 1 errors during collection !*",
+            "*! Interrupted: 1 error during collection !*",
             "*= 1 error in *",
         ]
     )
diff --git a/testing/test_doctest.py b/testing/test_doctest.py
index 37b3988f7..79095e3e7 100644
--- a/testing/test_doctest.py
+++ b/testing/test_doctest.py
@@ -334,7 +334,7 @@ class TestDoctests:
             [
                 "*ERROR collecting hello.py*",
                 "*{e}: No module named *asdals*".format(e=MODULE_NOT_FOUND_ERROR),
-                "*Interrupted: 1 errors during collection*",
+                "*Interrupted: 1 error during collection*",
             ]
         )
 
diff --git a/testing/test_mark.py b/testing/test_mark.py
index c8d5851ac..93bc77a16 100644
--- a/testing/test_mark.py
+++ b/testing/test_mark.py
@@ -891,7 +891,7 @@ def test_parameterset_for_fail_at_collect(testdir):
     result = testdir.runpytest(str(p1))
     result.stdout.fnmatch_lines(
         [
-            "collected 0 items / 1 errors",
+            "collected 0 items / 1 error",
             "* ERROR collecting test_parameterset_for_fail_at_collect.py *",
             "Empty parameter set in 'test' at line 3",
             "*= 1 error in *",
diff --git a/testing/test_runner_xunit.py b/testing/test_runner_xunit.py
index 1e63bbf49..0ff508d2c 100644
--- a/testing/test_runner_xunit.py
+++ b/testing/test_runner_xunit.py
@@ -234,7 +234,7 @@ def test_setup_funcarg_setup_when_outer_scope_fails(testdir):
             "*ValueError*42*",
             "*function2*",
             "*ValueError*42*",
-            "*2 error*",
+            "*2 errors*",
         ]
     )
     result.stdout.no_fnmatch_line("*xyz43*")
diff --git a/testing/test_skipping.py b/testing/test_skipping.py
index 51b1bbdd6..8ba77ba12 100644
--- a/testing/test_skipping.py
+++ b/testing/test_skipping.py
@@ -886,7 +886,7 @@ def test_errors_in_xfail_skip_expressions(testdir):
             "    syntax error",
             markline,
             "SyntaxError: invalid syntax",
-            "*1 pass*2 error*",
+            "*1 pass*2 errors*",
         ]
     )
 
diff --git a/testing/test_stepwise.py b/testing/test_stepwise.py
index f61425b6b..3e4f86f21 100644
--- a/testing/test_stepwise.py
+++ b/testing/test_stepwise.py
@@ -164,7 +164,7 @@ def test_stop_on_collection_errors(broken_testdir, broken_first):
     if broken_first:
         files.reverse()
     result = broken_testdir.runpytest("-v", "--strict-markers", "--stepwise", *files)
-    result.stdout.fnmatch_lines("*errors during collection*")
+    result.stdout.fnmatch_lines("*error during collection*")
 
 
 def test_xfail_handling(testdir):
diff --git a/testing/test_terminal.py b/testing/test_terminal.py
index c53b9f2ec..ba1844fed 100644
--- a/testing/test_terminal.py
+++ b/testing/test_terminal.py
@@ -1237,7 +1237,7 @@ def test_terminal_summary_warnings_header_once(testdir):
             "*= warnings summary =*",
             "*warning_from_test*",
             "*= short test summary info =*",
-            "*== 1 failed, 1 warnings in *",
+            "*== 1 failed, 1 warning in *",
         ]
     )
     result.stdout.no_fnmatch_line("*None*")
@@ -1263,6 +1263,7 @@ def test_terminal_summary_warnings_header_once(testdir):
             {"failed": (1,), "passed": (1,)},
         ),
         ("red", [("1 error", {"bold": True, "red": True})], {"error": (1,)}),
+        ("red", [("2 errors", {"bold": True, "red": True})], {"error": (1, 2)}),
         (
             "red",
             [
@@ -1281,16 +1282,12 @@ def test_terminal_summary_warnings_header_once(testdir):
             ],
             {"weird": (1,), "passed": (1,)},
         ),
-        (
-            "yellow",
-            [("1 warnings", {"bold": True, "yellow": True})],
-            {"warnings": (1,)},
-        ),
+        ("yellow", [("1 warning", {"bold": True, "yellow": True})], {"warnings": (1,)}),
         (
             "yellow",
             [
                 ("1 passed", {"bold": False, "green": True}),
-                ("1 warnings", {"bold": True, "yellow": True}),
+                ("1 warning", {"bold": True, "yellow": True}),
             ],
             {"warnings": (1,), "passed": (1,)},
         ),
diff --git a/testing/test_warnings.py b/testing/test_warnings.py
index 077636c52..bbcf87e5a 100644
--- a/testing/test_warnings.py
+++ b/testing/test_warnings.py
@@ -142,7 +142,7 @@ def test_unicode(testdir, pyfile_with_warnings):
         [
             "*== %s ==*" % WARNINGS_SUMMARY_HEADER,
             "*test_unicode.py:7: UserWarning: \u6d4b\u8bd5*",
-            "* 1 passed, 1 warnings*",
+            "* 1 passed, 1 warning*",
         ]
     )
 
@@ -201,7 +201,7 @@ def test_filterwarnings_mark(testdir, default_config):
     """
     )
     result = testdir.runpytest("-W always" if default_config == "cmdline" else "")
-    result.stdout.fnmatch_lines(["*= 1 failed, 2 passed, 1 warnings in *"])
+    result.stdout.fnmatch_lines(["*= 1 failed, 2 passed, 1 warning in *"])
 
 
 def test_non_string_warning_argument(testdir):
@@ -216,7 +216,7 @@ def test_non_string_warning_argument(testdir):
         """
     )
     result = testdir.runpytest("-W", "always")
-    result.stdout.fnmatch_lines(["*= 1 passed, 1 warnings in *"])
+    result.stdout.fnmatch_lines(["*= 1 passed, 1 warning in *"])
 
 
 def test_filterwarnings_mark_registration(testdir):
@@ -302,7 +302,7 @@ def test_collection_warnings(testdir):
             "*== %s ==*" % WARNINGS_SUMMARY_HEADER,
             "  *collection_warnings.py:3: UserWarning: collection warning",
             '    warnings.warn(UserWarning("collection warning"))',
-            "* 1 passed, 1 warnings*",
+            "* 1 passed, 1 warning*",
         ]
     )
 
@@ -358,7 +358,7 @@ def test_hide_pytest_internal_warnings(testdir, ignore_pytest_warnings):
             [
                 "*== %s ==*" % WARNINGS_SUMMARY_HEADER,
                 "*test_hide_pytest_internal_warnings.py:4: PytestWarning: some internal warning",
-                "* 1 passed, 1 warnings *",
+                "* 1 passed, 1 warning *",
             ]
         )
 
@@ -476,7 +476,7 @@ class TestDeprecationWarningsByDefault:
             [
                 "*== %s ==*" % WARNINGS_SUMMARY_HEADER,
                 "*test_hidden_by_mark.py:3: DeprecationWarning: collection",
-                "* 1 passed, 1 warnings*",
+                "* 1 passed, 1 warning*",
             ]
         )