diff --git a/block-storage/src/main/java/org/lucares/pdb/map/PersistentMap.java b/block-storage/src/main/java/org/lucares/pdb/map/PersistentMap.java
index 44dac17..09a1aaf 100644
--- a/block-storage/src/main/java/org/lucares/pdb/map/PersistentMap.java
+++ b/block-storage/src/main/java/org/lucares/pdb/map/PersistentMap.java
@@ -141,20 +141,20 @@ public class PersistentMap<K, V> implements AutoCloseable {
 		}
 	}
 
-	public void putAllValues(final Map<K, V> map) throws IOException {
+	public synchronized void putAllValues(final Map<K, V> map) throws IOException {
 		for (final Entry<K, V> e : map.entrySet()) {
 			putValue(e.getKey(), e.getValue());
 		}
 	}
 
-	public V putValue(final K key, final V value) throws IOException {
+	public synchronized V putValue(final K key, final V value) throws IOException {
 		final byte[] encodedKey = keyEncoder.encode(key);
 		final byte[] encodedValue = valueEncoder.encode(value);
 		final byte[] oldValue = putValue(encodedKey, encodedValue);
 		return oldValue == null ? null : valueEncoder.decode(oldValue);
 	}
 
-	public V getValue(final K key) throws IOException {
+	public synchronized V getValue(final K key) throws IOException {
 		final byte[] encodedKey = keyEncoder.encode(key);
 		final byte[] foundValue = getValue(encodedKey);
 		return foundValue == null ? null : valueEncoder.decode(foundValue);
@@ -311,7 +311,7 @@ public class PersistentMap<K, V> implements AutoCloseable {
 		diskBlock.force();
 	}
 
-	public void print() throws IOException {
+	public synchronized void print() throws IOException {
 
 		visitNodeEntriesPreOrder((node, parentNode, nodeEntry, depth) -> {
 
@@ -324,7 +324,7 @@ public class PersistentMap<K, V> implements AutoCloseable {
 		});
 	}
 
-	public void visitNodeEntriesPreOrder(final VisitorCallback visitor) throws IOException {
+	public synchronized void visitNodeEntriesPreOrder(final VisitorCallback visitor) throws IOException {
 		final long rootNodeOffset = readNodeOffsetOfRootNode();
 		visitNodeEntriesPreOrderRecursively(rootNodeOffset, null, visitor, 0);
 	}
@@ -347,7 +347,7 @@ public class PersistentMap<K, V> implements AutoCloseable {
 		FIND, ITERATE
 	}
 
-	public void visitValues(final K keyPrefix, final Visitor<K, V> visitor) throws IOException {
+	public synchronized void visitValues(final K keyPrefix, final Visitor<K, V> visitor) throws IOException {
 		final byte[] encodedKeyPrefix = keyEncoder.encode(keyPrefix);
 
 		final long rootNodeOffset = readNodeOffsetOfRootNode();