--- old/src/jdk.jdi/share/classes/com/sun/tools/jdi/EventSetImpl.java	2020-04-13 21:04:07.000000000 -0700
+++ new/src/jdk.jdi/share/classes/com/sun/tools/jdi/EventSetImpl.java	2020-04-13 21:04:07.000000000 -0700
@@ -425,16 +425,18 @@
         }
 
         public String className() {
-            String name = classSignature.substring(1, classSignature.length() - 1);
-            int index = name.indexOf(".");  // check if it's a hidden class
-            if (index < 0) {
-                name = name.replace('/', '.');
+            int index = classSignature.indexOf(";");
+            if (index == classSignature.length()) {
+                // trim leading 'L' and trailing ';'
+                return classSignature.substring(1, classSignature.length() - 1)
+                                     .replace('/', '.');
             } else {
-                // the class name of a hidden class is <binary-name> + "/" + <suffix>
-                name = name.substring(0, index).replace('/', '.') + "/" +
-                         name.substring(index + 1, name.length());
+                // type descriptor of a hidden class is "L" + N + ";" + "/" + <suffix>
+                // the class name is mapped to: N.replace('/', '.') + "/" + <suffix>
+                return classSignature.substring(1, index)
+                                     .replace('/', '.')
+                       + classSignature.substring(index+1);  // skip ';'
             }
-            return name;
         }
 
         public String classSignature() {