diff --git a/aegisub/libaegisub/include/libaegisub/line_iterator.h b/aegisub/libaegisub/include/libaegisub/line_iterator.h
index c26df9630..43e88f03e 100644
--- a/aegisub/libaegisub/include/libaegisub/line_iterator.h
+++ b/aegisub/libaegisub/include/libaegisub/line_iterator.h
@@ -71,8 +71,7 @@ public:
 	, lf('\n')
 	, width(1)
 	{
-		boost::to_lower(encoding);
-		if (encoding != "utf-8") {
+		if (boost::to_lower_copy(encoding) != "utf-8") {
 			agi::charset::IconvWrapper c("utf-8", encoding.c_str());
 			c.Convert("\r", 1, reinterpret_cast<char *>(&cr), sizeof(int));
 			c.Convert("\n", 1, reinterpret_cast<char *>(&lf), sizeof(int));