Index: /trunk/src/org/openstreetmap/josm/data/validation/tests/TagChecker.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/validation/tests/TagChecker.java	(revision 17476)
+++ /trunk/src/org/openstreetmap/josm/data/validation/tests/TagChecker.java	(revision 17477)
@@ -484,4 +484,5 @@
             || c == 0x0263 || c == 0x0194 // "ɣ/Ɣ" (U+0263/U+0194), see #18740
             || c == 0x0268 || c == 0x0197 // "ɨ/Ɨ" (U+0268/U+0197), see #18740
+            || c == 0x0269 || c == 0x0196 // "ɩ/Ɩ" (U+0269/U+0196), see #20437
             || c == 0x0272 || c == 0x019D // "ɲ/Ɲ" (U+0272/U+019D), see #18740
             || c == 0x0273 || c == 0x019E // "ŋ/Ŋ" (U+0273/U+019E), see #18740
Index: /trunk/test/unit/org/openstreetmap/josm/data/validation/tests/TagCheckerTest.java
===================================================================
--- /trunk/test/unit/org/openstreetmap/josm/data/validation/tests/TagCheckerTest.java	(revision 17476)
+++ /trunk/test/unit/org/openstreetmap/josm/data/validation/tests/TagCheckerTest.java	(revision 17477)
@@ -374,3 +374,12 @@
         assertEquals(0, errors.size());
     }
+
+    /**
+     * Non-regression test for <a href="https://josm.openstreetmap.de/ticket/20437">Bug #20437</a>.
+     */
+    @Test
+    void testTicket20437() {
+        assertFalse(TagChecker.containsUnusualUnicodeCharacter("name:kbp", "Wasɩŋtɔŋ"));
+        assertFalse(TagChecker.containsUnusualUnicodeCharacter("name:kbp", "Kalɩfɔrnii"));
+    }
 }