diff --git a/smack-experimental/src/main/java/org/jivesoftware/smackx/jingle_filetransfer/JingleFileTransferManager.java b/smack-experimental/src/main/java/org/jivesoftware/smackx/jingle_filetransfer/JingleFileTransferManager.java
index 7b96cdbd4..a50ea0519 100644
--- a/smack-experimental/src/main/java/org/jivesoftware/smackx/jingle_filetransfer/JingleFileTransferManager.java
+++ b/smack-experimental/src/main/java/org/jivesoftware/smackx/jingle_filetransfer/JingleFileTransferManager.java
@@ -32,7 +32,7 @@ public final class JingleFileTransferManager extends Manager {
         super(connection);
     }
 
-    public static JingleFileTransferManager getInstanceFor(XMPPConnection connection) {
+    public static synchronized JingleFileTransferManager getInstanceFor(XMPPConnection connection) {
         JingleFileTransferManager manager = INSTANCES.get(connection);
         if (manager == null) {
             manager = new JingleFileTransferManager(connection);
diff --git a/smack-experimental/src/main/java/org/jivesoftware/smackx/reference/ReferenceManager.java b/smack-experimental/src/main/java/org/jivesoftware/smackx/reference/ReferenceManager.java
index d3bdfce12..b588aa5e3 100644
--- a/smack-experimental/src/main/java/org/jivesoftware/smackx/reference/ReferenceManager.java
+++ b/smack-experimental/src/main/java/org/jivesoftware/smackx/reference/ReferenceManager.java
@@ -51,7 +51,7 @@ public final class ReferenceManager extends Manager {
      * @param connection xmpp connection
      * @return reference manager instance
      */
-    public static ReferenceManager getInstanceFor(XMPPConnection connection) {
+    public static synchronized ReferenceManager getInstanceFor(XMPPConnection connection) {
         ReferenceManager manager = INSTANCES.get(connection);
         if (manager == null) {
             manager = new ReferenceManager(connection);
diff --git a/smack-experimental/src/main/java/org/jivesoftware/smackx/sid/StableUniqueStanzaIdManager.java b/smack-experimental/src/main/java/org/jivesoftware/smackx/sid/StableUniqueStanzaIdManager.java
index 99ec03f5d..a9fd4fcfa 100644
--- a/smack-experimental/src/main/java/org/jivesoftware/smackx/sid/StableUniqueStanzaIdManager.java
+++ b/smack-experimental/src/main/java/org/jivesoftware/smackx/sid/StableUniqueStanzaIdManager.java
@@ -78,7 +78,7 @@ public final class StableUniqueStanzaIdManager extends Manager {
      * @param connection xmpp-connection
      * @return manager instance for the connection
      */
-    public static StableUniqueStanzaIdManager getInstanceFor(XMPPConnection connection) {
+    public static synchronized StableUniqueStanzaIdManager getInstanceFor(XMPPConnection connection) {
         StableUniqueStanzaIdManager manager = INSTANCES.get(connection);
         if (manager == null) {
             manager = new StableUniqueStanzaIdManager(connection);
diff --git a/smack-experimental/src/main/java/org/jivesoftware/smackx/spoiler/SpoilerManager.java b/smack-experimental/src/main/java/org/jivesoftware/smackx/spoiler/SpoilerManager.java
index f3bb80c85..fa5c8680b 100644
--- a/smack-experimental/src/main/java/org/jivesoftware/smackx/spoiler/SpoilerManager.java
+++ b/smack-experimental/src/main/java/org/jivesoftware/smackx/spoiler/SpoilerManager.java
@@ -61,7 +61,7 @@ public final class SpoilerManager extends Manager {
      * @param connection xmpp connection
      * @return SpoilerManager
      */
-    public static SpoilerManager getInstanceFor(XMPPConnection connection) {
+    public static synchronized SpoilerManager getInstanceFor(XMPPConnection connection) {
         SpoilerManager manager = INSTANCES.get(connection);
         if (manager == null) {
             manager = new SpoilerManager(connection);
diff --git a/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/JingleTransportMethodManager.java b/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/JingleTransportMethodManager.java
index 848dc1671..9a9941a07 100644
--- a/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/JingleTransportMethodManager.java
+++ b/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/JingleTransportMethodManager.java
@@ -48,7 +48,7 @@ public final class JingleTransportMethodManager extends Manager {
         super(connection);
     }
 
-    public static JingleTransportMethodManager getInstanceFor(XMPPConnection connection) {
+    public static synchronized JingleTransportMethodManager getInstanceFor(XMPPConnection connection) {
         JingleTransportMethodManager manager = INSTANCES.get(connection);
         if (manager == null) {
             manager = new JingleTransportMethodManager(connection);
diff --git a/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/transports/jingle_ibb/JingleIBBTransportManager.java b/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/transports/jingle_ibb/JingleIBBTransportManager.java
index 500a7b0a8..63dada1ae 100644
--- a/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/transports/jingle_ibb/JingleIBBTransportManager.java
+++ b/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/transports/jingle_ibb/JingleIBBTransportManager.java
@@ -38,7 +38,7 @@ public final class JingleIBBTransportManager extends JingleTransportManager<Jing
         JingleContentProviderManager.addJingleContentTransportProvider(getNamespace(), new JingleIBBTransportProvider());
     }
 
-    public static JingleIBBTransportManager getInstanceFor(XMPPConnection connection) {
+    public static synchronized JingleIBBTransportManager getInstanceFor(XMPPConnection connection) {
         JingleIBBTransportManager manager = INSTANCES.get(connection);
         if (manager == null) {
             manager = new JingleIBBTransportManager(connection);
diff --git a/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/transports/jingle_s5b/JingleS5BTransportManager.java b/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/transports/jingle_s5b/JingleS5BTransportManager.java
index 2274aaac7..52c4289a6 100644
--- a/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/transports/jingle_s5b/JingleS5BTransportManager.java
+++ b/smack-extensions/src/main/java/org/jivesoftware/smackx/jingle/transports/jingle_s5b/JingleS5BTransportManager.java
@@ -63,7 +63,7 @@ public final class JingleS5BTransportManager extends JingleTransportManager<Jing
         JingleContentProviderManager.addJingleContentTransportProvider(getNamespace(), new JingleS5BTransportProvider());
     }
 
-    public static JingleS5BTransportManager getInstanceFor(XMPPConnection connection) {
+    public static synchronized JingleS5BTransportManager getInstanceFor(XMPPConnection connection) {
         JingleS5BTransportManager manager = INSTANCES.get(connection);
         if (manager == null) {
             manager = new JingleS5BTransportManager(connection);
diff --git a/smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/JingleSession.java b/smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/JingleSession.java
index c7f7b2683..91e2ff035 100644
--- a/smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/JingleSession.java
+++ b/smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/JingleSession.java
@@ -620,7 +620,7 @@ public class JingleSession extends JingleNegotiator implements MediaReceivedList
      *            A XMPP connection
      * @return a Jingle session
      */
-    public static JingleSession getInstanceFor(XMPPConnection con) {
+    public static synchronized JingleSession getInstanceFor(XMPPConnection con) {
         if (con == null) {
             throw new IllegalArgumentException("XMPPConnection cannot be null");
         }