diff --git a/bin/tests/system/idna/tests.sh b/bin/tests/system/idna/tests.sh
index b4aaf6e71b..19a086dff2 100644
--- a/bin/tests/system/idna/tests.sh
+++ b/bin/tests/system/idna/tests.sh
@@ -11,9 +11,13 @@ SYSTEMTESTTOP=..
 . $SYSTEMTESTTOP/conf.sh
 
 # Set known locale for the tests
-LC_ALL="en_US.UTF-8"
-export LC_ALL
 
+if locale -a | grep -qE "^C\\.(UTF-8|utf8)"; then
+    LC_ALL="C.UTF-8"
+elif locale -a | grep -qE "^en_US\\.(UTF-8|utf8)"; then
+    LC_ALL="en_US.UTF-8"
+fi
+export LC_ALL
 
 # This set of tests check the behavior of the IDNA options in "dig".
 #