--- old/src/java.desktop/share/classes/sun/font/SunFontManager.java	2019-10-07 15:23:18.816940910 +0900
+++ new/src/java.desktop/share/classes/sun/font/SunFontManager.java	2019-10-07 15:23:18.272951880 +0900
@@ -1077,8 +1077,11 @@
              * trying to gracefully handle/recover from a system
              * misconfiguration and this is probably a reasonable substitution.
              */
-            defaultPhysicalFont = (PhysicalFont)
+            Font2D font2d =
                 findFont2D(getDefaultFontFaceName(), Font.PLAIN, NO_FALLBACK);
+            if (font2d instanceof PhysicalFont) {
+                defaultPhysicalFont = (PhysicalFont) font2d;
+            }
             if (defaultPhysicalFont == null) {
                 /* Because of the findFont2D call above, if we reach here, we
                  * know all fonts have already been loaded, just accept any
@@ -1089,6 +1092,9 @@
                 Iterator<PhysicalFont> i = physicalFonts.values().iterator();
                 if (i.hasNext()) {
                     defaultPhysicalFont = i.next();
+                    if (font2d instanceof CompositeFont) {
+                        defaultPhysicalFont = ((CompositeFont) font2d).getSlotFont(0);
+                    }
                 } else {
                     throw new Error("Probable fatal error:No fonts found.");
                 }
--- /dev/null	2019-08-19 21:12:08.834025527 +0900
+++ new/test/jdk/java/awt/font/DefaultFontTest/DefaultFontTest.java	2019-10-07 15:23:19.129934598 +0900
@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8221741
+ * @modules java.desktop/sun.font:open
+ * @requires (os.family == "linux") | (os.family == "aix")
+ * @summary ClassCastException happen when fontconfig.properties was used
+ */
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+
+public class DefaultFontTest {
+    public static void main(String[] args) throws Exception {
+        Class<?> SunFontManager_clz = Class.forName("sun.font.SunFontManager");
+        Method getInstance_mid = SunFontManager_clz.getDeclaredMethod("getInstance");
+        Object sfm = getInstance_mid.invoke(null);
+        Field defaultFontName_fid = SunFontManager_clz.getDeclaredField("defaultFontName");
+        defaultFontName_fid.setAccessible(true);
+        defaultFontName_fid.set(sfm, "Dialog");
+        Method loadFonts_mid = SunFontManager_clz.getDeclaredMethod("loadFonts");
+        loadFonts_mid.setAccessible(true);
+        loadFonts_mid.invoke(sfm);
+        Method getDefaultPhysicalFont_mid = sfm.getClass().getMethod("getDefaultPhysicalFont");
+        Object physicalFont = getDefaultPhysicalFont_mid.invoke(sfm);
+        System.out.println(physicalFont);
+    }
+}