diff --git a/src/mathed/InsetMath.C b/src/mathed/InsetMath.C
index 9b203d2f59..e44c384101 100644
--- a/src/mathed/InsetMath.C
+++ b/src/mathed/InsetMath.C
@@ -82,7 +82,7 @@ void InsetMath::write(WriteStream & os) const
 }
 
 
-int InsetMath::plaintext(Buffer const &, odocstream & os,
+int InsetMath::plaintext(Buffer const &, odocstream &,
                          OutputParams const &) const
 {
 	// all math plain text output shall take place in InsetMathHull