--- a/src/hotspot/share/classfile/classFileParser.cpp	Wed Jun 19 12:25:12 2019 +0200
+++ b/src/hotspot/share/classfile/classFileParser.cpp	Wed Jun 19 08:42:15 2019 -0400
@@ -4956,6 +4956,7 @@
 bool ClassFileParser::verify_unqualified_name(const char* name,
                                               unsigned int length,
                                               int type) {
+  if (length == 0) return false;  // Must have at least one char.
   for (const char* p = name; p != name + length; p++) {
     switch(*p) {
       case '.':
@@ -5105,7 +5106,7 @@
           int newlen = c - (char*) signature;
           bool legal = verify_unqualified_name(signature, newlen, LegalClass);
           if (!legal) {
-            classfile_parse_error("Class name contains illegal character "
+            classfile_parse_error("Class name is empty or contains illegal character "
                                   "in descriptor in class file %s",
                                   CHECK_0);
             return NULL;

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/runtime/classFileParserBug/EmptyUnqName.jasm	Wed Jun 19 08:42:15 2019 -0400
@@ -0,0 +1,43 @@
+/*
+ * 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.
+ */
+
+super public class EmptyUnqName version 56:0 {
+
+    public Method "<init>":"()V" stack 1 locals 1 {
+        aload_0;
+        invokespecial Method java/lang/Object."<init>":"()V";
+        return;
+    }
+
+    public static Method main:"([Ljava/lang/String;)V" stack 2 locals 1 {
+        getstatic Field java/lang/System.out:"Ljava/io/PrintStream;";
+        ldc String "Testing method param types";
+        invokevirtual Method java/io/PrintStream.println:"(Ljava/lang/String;)V";
+        return;
+    }
+
+    public static Method func:"(L;)V" stack 0 locals 1 {
+        return;
+    }
+
+} // end Class EmptyUnqName

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/runtime/classFileParserBug/TestEmptyUnqName.java	Wed Jun 19 08:42:15 2019 -0400
@@ -0,0 +1,46 @@
+/*
+ * 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 8225789
+ * @summary Test that an unqualified name of "L;" causes a ClassFormatError exception.
+ * @compile EmptyUnqName.jasm
+ * @run main/othervm -Xverify:remote TestEmptyUnqName
+ */
+
+public class TestEmptyUnqName {
+    public static void main(String args[]) throws Throwable {
+
+        System.out.println("Regression test for bug 8225789");
+
+        try {
+            Class newClass = Class.forName("EmptyUnqName");
+            throw new RuntimeException("Expected ClassFormatError exception not thrown");
+        } catch (java.lang.ClassFormatError e) {
+            if (!e.getMessage().contains("Class name is empty or contains illegal character")) {
+                throw new RuntimeException("Wrong ClassFormatError: " + e.getMessage());
+            }
+        }
+    }
+}

--- a/test/hotspot/jtreg/runtime/verifier/TestSigParse.java	Wed Jun 19 12:25:12 2019 +0200
+++ b/test/hotspot/jtreg/runtime/verifier/TestSigParse.java	Wed Jun 19 08:42:15 2019 -0400
@@ -63,7 +63,7 @@
             throw new RuntimeException("Expected ClasFormatError exception not thrown");
         } catch (java.lang.ClassFormatError e) {
             String eMsg = e.getMessage();
-            if (!eMsg.contains("Class name contains illegal character")) {
+            if (!eMsg.contains("Class name is empty or contains illegal character")) {
                 throw new RuntimeException("Unexpected exception: " + eMsg);
             }
         }