diff --git a/_pytest/mark.py b/_pytest/mark.py
index 91aa3747e..2a4a0f265 100644
--- a/_pytest/mark.py
+++ b/_pytest/mark.py
@@ -272,8 +272,9 @@ class MarkGenerator:
             pass
         self._markers = l = set()
         for line in self._config.getini("markers"):
-            beginning = line.split(":", 1)
-            x = beginning[0].split("(", 1)[0]
+            marker, _ = line.split(":", 1)
+            marker = marker.rstrip()
+            x = marker.split("(", 1)[0]
             l.add(x)
         if name not in self._markers:
             raise AttributeError("%r not a registered marker" % (name,))
diff --git a/changelog/2856.bugfix b/changelog/2856.bugfix
new file mode 100644
index 000000000..7e5fc8fc7
--- /dev/null
+++ b/changelog/2856.bugfix
@@ -0,0 +1 @@
+Strip whitespace from marker names when reading them from INI config.
diff --git a/testing/test_mark.py b/testing/test_mark.py
index dc51bbac0..9ae88a665 100644
--- a/testing/test_mark.py
+++ b/testing/test_mark.py
@@ -169,6 +169,23 @@ def test_markers_option(testdir):
     ])
 
 
+def test_ini_markers_whitespace(testdir):
+    testdir.makeini("""
+        [pytest]
+        markers =
+            a1 : this is a whitespace marker
+    """)
+    testdir.makepyfile("""
+        import pytest
+
+        @pytest.mark.a1
+        def test_markers():
+            assert True
+    """)
+    rec = testdir.inline_run("--strict", "-m", "a1")
+    rec.assertoutcome(passed=1)
+
+
 def test_markers_option_with_plugin_in_current_dir(testdir):
     testdir.makeconftest('pytest_plugins = "flip_flop"')
     testdir.makepyfile(flip_flop="""\