diff --git a/indra/llcommon/llmutex.h b/indra/llcommon/llmutex.h
index 6e8cf9643b..62943845a5 100644
--- a/indra/llcommon/llmutex.h
+++ b/indra/llcommon/llmutex.h
@@ -194,6 +194,18 @@ public:
             mSharedMutex->unlock<SHARED>();
     }
 
+    void lock()
+    {
+        if (mSharedMutex)
+            mSharedMutex->lock<SHARED>();
+    }
+
+    void unlock()
+    {
+        if (mSharedMutex)
+            mSharedMutex->unlock<SHARED>();
+    }
+
 private:
     LLSharedMutex* mSharedMutex;
 };
diff --git a/indra/llimage/llimage.h b/indra/llimage/llimage.h
index 8b966b8ea3..6b14b68c78 100644
--- a/indra/llimage/llimage.h
+++ b/indra/llimage/llimage.h
@@ -179,7 +179,7 @@ private:
 
 public:
     template<bool SHARED>
-    class DataLock : LLSharedMutexLockTemplate<SHARED>
+    class DataLock : public LLSharedMutexLockTemplate<SHARED>
     {
     public:
         DataLock(const LLImageBase* image)
diff --git a/indra/newview/llsnapshotlivepreview.cpp b/indra/newview/llsnapshotlivepreview.cpp
index 0d0c025db0..ea95d71b27 100644
--- a/indra/newview/llsnapshotlivepreview.cpp
+++ b/indra/newview/llsnapshotlivepreview.cpp
@@ -894,7 +894,9 @@ LLPointer<LLImageRaw> LLSnapshotLivePreview::getEncodedImage()
         else
         {
             // Update mFormattedImage if necessary
-            getFormattedImage();
+            lock.unlock();
+            getFormattedImage(); // will apply filters to mPreviewImage with a lock
+            lock.lock();
             if (getSnapshotFormat() == LLSnapshotModel::SNAPSHOT_FORMAT_BMP)
             {
                 // BMP hack : copy instead of decode otherwise decode will crash.