diff --git a/app/src/processing/app/contrib/ContributionListing.java b/app/src/processing/app/contrib/ContributionListing.java
index 821601278..083f85685 100644
--- a/app/src/processing/app/contrib/ContributionListing.java
+++ b/app/src/processing/app/contrib/ContributionListing.java
@@ -36,7 +36,7 @@ public class ContributionListing {
   static final String LISTING_URL =
     "http://download.processing.org/contributions.txt";
 
-  static ContributionListing singleInstance;
+  static volatile ContributionListing singleInstance;
 
   File listingFile;
   ArrayList<ContributionChangeListener> listeners;
@@ -64,7 +64,11 @@ public class ContributionListing {
 
   static ContributionListing getInstance() {
     if (singleInstance == null) {
-      singleInstance = new ContributionListing();
+      synchronized (ContributionListing.class) {
+        if (singleInstance == null) {
+          singleInstance = new ContributionListing();
+        }
+      }
     }
     return singleInstance;
   }