diff --git a/src/main/java/com/raoulvdberge/refinedstorage/apiimpl/storage/StorageCacheFluid.java b/src/main/java/com/raoulvdberge/refinedstorage/apiimpl/storage/StorageCacheFluid.java
index 0393c8e3b..1900f12a4 100755
--- a/src/main/java/com/raoulvdberge/refinedstorage/apiimpl/storage/StorageCacheFluid.java
+++ b/src/main/java/com/raoulvdberge/refinedstorage/apiimpl/storage/StorageCacheFluid.java
@@ -77,7 +77,7 @@ public class StorageCacheFluid implements IStorageCache<FluidStack> {
     }
 
     @Override
-    public void flush() {
+    public synchronized void flush() {
         if (!batchedChanges.isEmpty()) {
             batchedChanges.forEach(c -> listeners.forEach(l -> l.onChanged(c.getKey(), c.getValue())));
             batchedChanges.clear();
diff --git a/src/main/java/com/raoulvdberge/refinedstorage/apiimpl/storage/StorageCacheItem.java b/src/main/java/com/raoulvdberge/refinedstorage/apiimpl/storage/StorageCacheItem.java
index ec08d38ac..d3e7c3120 100755
--- a/src/main/java/com/raoulvdberge/refinedstorage/apiimpl/storage/StorageCacheItem.java
+++ b/src/main/java/com/raoulvdberge/refinedstorage/apiimpl/storage/StorageCacheItem.java
@@ -79,7 +79,7 @@ public class StorageCacheItem implements IStorageCache<ItemStack> {
     }
 
     @Override
-    public void flush() {
+    public synchronized void flush() {
         if (!batchedChanges.isEmpty()) {
             batchedChanges.forEach(c -> listeners.forEach(l -> l.onChanged(c.getKey(), c.getValue())));
             batchedChanges.clear();