diff --git a/src/main/java/hudson/security/LDAPSecurityRealm.java b/src/main/java/hudson/security/LDAPSecurityRealm.java
index ef01aa6b..b1f532ef 100644
--- a/src/main/java/hudson/security/LDAPSecurityRealm.java
+++ b/src/main/java/hudson/security/LDAPSecurityRealm.java
@@ -96,6 +96,7 @@
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -1535,7 +1536,7 @@ public FormValidation doValidate(StaplerRequest req) throws Exception {
                 return FormValidation.ok();
             }
             // extract the submitted details
-            JSONObject json = JSONObject.fromObject(IOUtils.toString(req.getInputStream(), Charset.defaultCharset()));
+            JSONObject json = JSONObject.fromObject(IOUtils.toString(req.getInputStream(), Util.fixNull(req.getCharacterEncoding(), StandardCharsets.UTF_8.name())));
             String user = json.getString("testUser");
             String password = json.getString("testPassword");
             JSONObject realmCfg;