diff --git a/testsuite/ctk/textbuffer.c b/testsuite/ctk/textbuffer.c
index ef221f707f..67377a7685 100644
--- a/testsuite/ctk/textbuffer.c
+++ b/testsuite/ctk/textbuffer.c
@@ -120,7 +120,7 @@ count_toggles_at_iter (CtkTextIter *iter,
 }
 
 static gint
-count_toggles_in_range_by_char (CtkTextBuffer     *buffer,
+count_toggles_in_range_by_char (CtkTextBuffer     *buffer G_GNUC_UNUSED,
                                 CtkTextTag        *of_tag,
                                 const CtkTextIter *start,
                                 const CtkTextIter *end)