1 files changed, 1 insertions, 1 deletions
diff --git a/src/diff.h b/src/diff.h
index 578c4ea..a64f0d3 100644
--- a/src/diff.h
+++ b/src/diff.h
@@ -361,7 +361,7 @@ extern void print_sdiff_script (struct change *);
 extern char const change_letter[4];
 extern char const pr_program[];
 extern char *concat (char const *, char const *, char const *);
-extern bool lines_differ (char const *, char const *);
+extern bool lines_differ (char const *, char const *) _GL_ATTRIBUTE_PURE;
 extern lin translate_line_number (struct file_data const *, lin);
 extern struct change *find_change (struct change *);
 extern struct change *find_reverse_change (struct change *);