diff --git a/util/has_lib.sh b/util/has_lib.sh
index 6be2cf9..75e216c 100755
--- a/util/has_lib.sh
+++ b/util/has_lib.sh
@@ -53,7 +53,7 @@ case "$1" in
     result=$?
     ;;
   *)
-    echo "Unknown library: $1"
+    >&2 echo "Unknown library: $1"
     exit 1
 esac