diff --git a/Lib/test/test_warnings/__init__.py b/Lib/test/test_warnings/__init__.py
index e007dc7..f2fdaa5 100644
--- a/Lib/test/test_warnings/__init__.py
+++ b/Lib/test/test_warnings/__init__.py
@@ -125,6 +125,7 @@
             self.module.filterwarnings("ignore", category=UserWarning)
             self.module.warn("FilterTests.test_ignore", UserWarning)
             self.assertEqual(len(w), 0)
+            self.assertEqual(list(__warningregistry__), ['version'])
 
     def test_ignore_after_default(self):
         with original_warnings.catch_warnings(record=True,
diff --git a/Lib/warnings.py b/Lib/warnings.py
index c4bb22e..d7ea057 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -364,7 +364,6 @@
         action = defaultaction
     # Early exit actions
     if action == "ignore":
-        registry[key] = 1
         return
 
     # Prime the linecache for formatting, in case the
diff --git a/Misc/NEWS.d/next/Library/2017-11-21-16-05-35.bpo-27535.JLhcNz.rst b/Misc/NEWS.d/next/Library/2017-11-21-16-05-35.bpo-27535.JLhcNz.rst
new file mode 100644
index 0000000..51bcfb7
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-11-21-16-05-35.bpo-27535.JLhcNz.rst
@@ -0,0 +1,4 @@
+The warnings module doesn't leak memory anymore in the hidden warnings
+registry for the "ignore" action of warnings filters. warn_explicit()
+function doesn't add the warning key to the registry anymore for the
+"ignore" action.
diff --git a/Python/_warnings.c b/Python/_warnings.c
index 27f5b81..2937036 100644
--- a/Python/_warnings.c
+++ b/Python/_warnings.c
@@ -528,16 +528,21 @@
         goto cleanup;
     }
 
+    if (_PyUnicode_EqualToASCIIString(action, "ignore")) {
+        goto return_none;
+    }
+
     /* Store in the registry that we've been here, *except* when the action
        is "always". */
     rc = 0;
     if (!_PyUnicode_EqualToASCIIString(action, "always")) {
         if (registry != NULL && registry != Py_None &&
-                PyDict_SetItem(registry, key, Py_True) < 0)
+            PyDict_SetItem(registry, key, Py_True) < 0)
+        {
             goto cleanup;
-        else if (_PyUnicode_EqualToASCIIString(action, "ignore"))
-            goto return_none;
-        else if (_PyUnicode_EqualToASCIIString(action, "once")) {
+        }
+
+        if (_PyUnicode_EqualToASCIIString(action, "once")) {
             if (registry == NULL || registry == Py_None) {
                 registry = get_once_registry();
                 if (registry == NULL)