diff --git a/jdk/src/share/classes/java/lang/ClassLoader.java b/jdk/src/share/classes/java/lang/ClassLoader.java
index df3c312834..9aeb53e324 100644
--- a/jdk/src/share/classes/java/lang/ClassLoader.java
+++ b/jdk/src/share/classes/java/lang/ClassLoader.java
@@ -1706,10 +1706,14 @@ protected Package definePackage(String name, String specTitle,
         throws IllegalArgumentException
     {
         Objects.requireNonNull(name);
-        Package pkg = new Package(name, specTitle, specVersion, specVendor,
-                implTitle, implVersion, implVendor,
-                sealBase, this);
-        if (packages.putIfAbsent(name, pkg) != null) {
+        Package pkg = getPackage(name);
+        if (pkg != null) {
+            throw new IllegalArgumentException(name);
+        }
+        final Package new_pkg = new Package(name, specTitle, specVersion, specVendor,
+                          implTitle, implVersion, implVendor,
+                          sealBase, this);
+        if (packages.computeIfAbsent(name, key -> new_pkg) != new_pkg) {
             throw new IllegalArgumentException(name);
         }
         return pkg;