diff --git a/WHATSNEW b/WHATSNEW
index 95800a56f..d001045d4 100644
--- a/WHATSNEW
+++ b/WHATSNEW
@@ -14,6 +14,7 @@ Fixed bugs:
   Bugzilla report 40207.
 * Macro element did not include top level Text. Bugzilla report 36803.
 * AntClassLoader did not isolate resources when isolate was set. Bugzilla report 38747.
+* Diagnostics broken when using java 1.4. Bugzilla report 40395.
 
 Other changes:
 --------------
diff --git a/src/main/org/apache/tools/ant/Diagnostics.java b/src/main/org/apache/tools/ant/Diagnostics.java
index 3ae771d04..f4a376922 100644
--- a/src/main/org/apache/tools/ant/Diagnostics.java
+++ b/src/main/org/apache/tools/ant/Diagnostics.java
@@ -600,8 +600,12 @@ public final class Diagnostics {
         printProperty(out, ProxySetup.SOCKS_PROXY_PORT);
         printProperty(out, ProxySetup.SOCKS_PROXY_USERNAME);
         printProperty(out, ProxySetup.SOCKS_PROXY_PASSWORD);
-        
-        final String proxyDiagClassname="org.apache.tools.ant.util.java15.ProxyDiagnostics";
+
+        if (JavaEnvUtils.getJavaVersionNumber() < 15) {
+            return;
+        }
+        final String proxyDiagClassname
+            = "org.apache.tools.ant.util.java15.ProxyDiagnostics";
         try {
             Class proxyDiagClass = Class.forName(proxyDiagClassname);
             Object instance =proxyDiagClass.newInstance();
@@ -611,12 +615,11 @@ public final class Diagnostics {
             //not included, do nothing
         } catch (IllegalAccessException e) {
             //not included, do nothing
-
         } catch (InstantiationException e) {
             //not included, do nothing
-
+        } catch (NoClassDefFoundError e) {
+            // not included, to nothing
         }
-
     }
 
 }