diff --git a/pmd-apex/src/main/java/net/sourceforge/pmd/lang/apex/rule/security/ApexOpenRedirectRule.java b/pmd-apex/src/main/java/net/sourceforge/pmd/lang/apex/rule/security/ApexOpenRedirectRule.java
index 111478d666..16008dd90d 100644
--- a/pmd-apex/src/main/java/net/sourceforge/pmd/lang/apex/rule/security/ApexOpenRedirectRule.java
+++ b/pmd-apex/src/main/java/net/sourceforge/pmd/lang/apex/rule/security/ApexOpenRedirectRule.java
@@ -28,7 +28,7 @@ import net.sourceforge.pmd.lang.apex.rule.AbstractApexRule;
  */
 public class ApexOpenRedirectRule extends AbstractApexRule {
     private static final String PAGEREFERENCE = "PageReference";
-    private static final Set<String> listOfStringLiteralVariables = new HashSet<>();
+    private final Set<String> listOfStringLiteralVariables = new HashSet<>();
 
     public ApexOpenRedirectRule() {
         setProperty(CODECLIMATE_CATEGORIES, new String[] { "Security" });