diff --git a/src/support/Package.cpp b/src/support/Package.cpp
index 80615ed5cd..d97cbf9df6 100644
--- a/src/support/Package.cpp
+++ b/src/support/Package.cpp
@@ -363,6 +363,12 @@ FileName const get_locale_dir(FileName const & system_support_dir)
 	if (path.exists() && path.isDirectory())
 		return path;
 
+	// 4. Search for source tree "po/" in case LyX was launched with
+	// '-sysdir' argument.
+	path.set(addPath(system_support_dir.absFilename(), "../po"));
+	if (path.exists() && path.isDirectory())
+		return path;
+
 	return FileName();
 }