diff --git a/src/main/java/org/jastadd/relast/compiler/RelAstProcessor.java b/src/main/java/org/jastadd/relast/compiler/RelAstProcessor.java
index 4e3c97d120b8a1906b77b3d334fea536bdfa40bc..943583517f406e9b557e3bb34262b15185b38438 100644
--- a/src/main/java/org/jastadd/relast/compiler/RelAstProcessor.java
+++ b/src/main/java/org/jastadd/relast/compiler/RelAstProcessor.java
@@ -25,7 +25,7 @@ public abstract class RelAstProcessor extends AbstractCompiler {
     super(name, jastAddCompliant);
   }
 
-  protected static boolean isGrammarFile(String fileName) {
+  protected boolean isGrammarFile(String fileName) {
     String extension = fileName.subSequence(fileName.lastIndexOf('.'), fileName.length()).toString();
     return extension.equals(".relast") || extension.equals(".ast");
   }
diff --git a/src/main/java/org/jastadd/relast/compiler/RelastSourceToSourceCompiler.java b/src/main/java/org/jastadd/relast/compiler/RelastSourceToSourceCompiler.java
index e919ba822c44bee59b935bbc8d7e553c571101c9..7c394837fec649d30464cf882bc9578f205494a6 100644
--- a/src/main/java/org/jastadd/relast/compiler/RelastSourceToSourceCompiler.java
+++ b/src/main/java/org/jastadd/relast/compiler/RelastSourceToSourceCompiler.java
@@ -22,7 +22,8 @@ public class RelastSourceToSourceCompiler extends RelAstProcessor {
     }
   }
 
-  protected static boolean isGrammarFile(String fileName) {
+  @Override
+  protected boolean isGrammarFile(String fileName) {
     String extension = fileName.subSequence(fileName.lastIndexOf("."), fileName.length()).toString();
     return extension.equals(".relast") || extension.equals(".ast");
   }