diff --git a/src/main/java/it/cavallium/dbengine/lucene/CheckIndexInput.java b/src/main/java/it/cavallium/dbengine/lucene/CheckIndexInput.java
index fa4a282..65bc719 100644
--- a/src/main/java/it/cavallium/dbengine/lucene/CheckIndexInput.java
+++ b/src/main/java/it/cavallium/dbengine/lucene/CheckIndexInput.java
@@ -16,8 +16,8 @@ public class CheckIndexInput extends IndexInput {
 		this.input = input;
 	}
 
-	private void checkThread() {
-		LuceneUtils.checkLuceneThread();
+	private static void checkThread() {
+		assert LuceneUtils.isLuceneThread();
 	}
 
 	@Override
diff --git a/src/main/java/it/cavallium/dbengine/lucene/CheckIndexOutput.java b/src/main/java/it/cavallium/dbengine/lucene/CheckIndexOutput.java
index 2a4173f..65cdad3 100644
--- a/src/main/java/it/cavallium/dbengine/lucene/CheckIndexOutput.java
+++ b/src/main/java/it/cavallium/dbengine/lucene/CheckIndexOutput.java
@@ -14,8 +14,8 @@ public class CheckIndexOutput extends IndexOutput {
 		this.output = output;
 	}
 
-	private void checkThread() {
-		LuceneUtils.checkLuceneThread();
+	private static void checkThread() {
+		assert LuceneUtils.isLuceneThread();
 	}
 
 	@Override