diff --git a/core/src/main/java/jenkins/security/ResourceDomainConfiguration.java b/core/src/main/java/jenkins/security/ResourceDomainConfiguration.java
index a985273b30..f5465ca4b6 100644
--- a/core/src/main/java/jenkins/security/ResourceDomainConfiguration.java
+++ b/core/src/main/java/jenkins/security/ResourceDomainConfiguration.java
@@ -134,7 +134,7 @@ public final class ResourceDomainConfiguration extends GlobalConfiguration {
 
         StaplerRequest currentRequest = Stapler.getCurrentRequest();
         if (currentRequest != null) {
-            String currentRequestHost = currentRequest.getHeader("Host");
+            String currentRequestHost = currentRequest.getServerName();
 
             if (currentRequestHost.equals(resourceRootUrlHost)) {
                 return FormValidation.error(Messages.ResourceDomainConfiguration_SameAsCurrent());