diff --git a/core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/iterator/GroupIterator.java b/core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/iterator/GroupIterator.java
index 9bb0d51dfdf..943dde243fd 100644
--- a/core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/iterator/GroupIterator.java
+++ b/core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/iterator/GroupIterator.java
@@ -7,8 +7,6 @@
  *******************************************************************************/
 package org.eclipse.rdf4j.query.algebra.evaluation.iterator;
 
-import java.io.File;
-import java.io.IOException;
 import java.io.Serializable;
 import java.util.Collection;
 import java.util.HashSet;
@@ -51,6 +49,7 @@
 import org.eclipse.rdf4j.query.impl.EmptyBindingSet;
 import org.mapdb.DB;
 import org.mapdb.DBMaker;
+import org.mapdb.Serializer;
 
 /**
  * @author David Huynh
@@ -76,8 +75,6 @@ public class GroupIterator extends CloseableIteratorIteration<BindingSet, QueryE
 
 	private final Object lock = new Object();
 
-	private final File tempFile;
-
 	private final DB db;
 
 	/**
@@ -103,14 +100,12 @@ public GroupIterator(EvaluationStrategy strategy, Group group, BindingSet parent
 		this.iterationCacheSyncThreshold = iterationCacheSyncThreshold;
 
 		if (this.iterationCacheSyncThreshold > 0) {
-			try {
-				this.tempFile = File.createTempFile("group-eval", null);
-			} catch (IOException e) {
-				throw new QueryEvaluationException("could not initialize temp db", e);
-			}
-			this.db = DBMaker.newFileDB(tempFile).deleteFilesAfterClose().closeOnJvmShutdown().make();
+			this.db = DBMaker.tempFileDB()
+					.fileDeleteAfterClose()
+					.fileChannelEnable()
+					.closeOnJvmShutdown()
+					.make();
 		} else {
-			this.tempFile = null;
 			this.db = null;
 		}
 	}
@@ -158,7 +153,7 @@ protected void handleClose() throws QueryEvaluationException {
 
 	private <T> Set<T> createSet(String setName) {
 		if (db != null) {
-			return db.getHashSet(setName);
+			return (Set<T>) db.hashSet(setName).serializer(Serializer.JAVA).create();
 		} else {
 			return new HashSet<>();
 		}
diff --git a/pom.xml b/pom.xml
index ddbee47b31b..dc93aed594a 100644
--- a/pom.xml
+++ b/pom.xml
@@ -637,7 +637,7 @@
 			<dependency>
 				<groupId>org.mapdb</groupId>
 				<artifactId>mapdb</artifactId>
-				<version>1.0.8</version>
+				<version>3.0.8</version>
 			</dependency>
 		</dependencies>
 	</dependencyManagement>