diff --git a/src/_pytest/assertion/util.py b/src/_pytest/assertion/util.py
index c2a4e446f..d1a11d0bf 100644
--- a/src/_pytest/assertion/util.py
+++ b/src/_pytest/assertion/util.py
@@ -31,7 +31,6 @@ def format_explanation(explanation):
     for when one explanation needs to span multiple lines, e.g. when
     displaying diffs.
     """
-    explanation = explanation
     lines = _split_explanation(explanation)
     result = _format_lines(lines)
     return "\n".join(result)