diff --git a/test/vpp_pg_interface.py b/test/vpp_pg_interface.py
index a79af03..2256ada 100644
--- a/test/vpp_pg_interface.py
+++ b/test/vpp_pg_interface.py
@@ -148,7 +148,7 @@
         before = len(output.res)
         if filter_out_fn:
             output.res = [p for p in output.res if not filter_out_fn(p)]
-        removed = len(output.res) - before
+        removed = before - len(output.res)
         if removed:
             self.test.logger.debug(
                 "Filtered out %s packets from capture (returning %s)" %