diff --git a/src/main/java/azgracompress/compression/ImageCompressor.java b/src/main/java/azgracompress/compression/ImageCompressor.java
index d2012ee939ffa78422266162d222ffe6b2c82d4e..5728d6acece9024c4718a72d6086610e67193e7e 100644
--- a/src/main/java/azgracompress/compression/ImageCompressor.java
+++ b/src/main/java/azgracompress/compression/ImageCompressor.java
@@ -68,7 +68,8 @@ public class ImageCompressor extends CompressorDecompressorBase {
     }
 
     public int streamCompress(OutputStream outputStream) {
-
+        assert (false) : "Not implemented!";
+        return -1;
     }
 
     public boolean compress() {