diff --git a/materialbarcodescanner/src/main/java/com/edwardvanraak/materialbarcodescanner/CameraSource.java b/materialbarcodescanner/src/main/java/com/edwardvanraak/materialbarcodescanner/CameraSource.java
index b2160d9..2a89626 100644
--- a/materialbarcodescanner/src/main/java/com/edwardvanraak/materialbarcodescanner/CameraSource.java
+++ b/materialbarcodescanner/src/main/java/com/edwardvanraak/materialbarcodescanner/CameraSource.java
@@ -1071,8 +1071,10 @@ private class FrameProcessingRunnable implements Runnable {
         @SuppressLint("Assert")
         void release() {
             assert (mProcessingThread.getState() == State.TERMINATED);
-            mDetector.release();
-            mDetector = null;
+            if (mDetector != null) {
+                mDetector.release();
+                mDetector = null;
+            }
         }
 
         /**