diff --git a/bootstrap b/bootstrap
index 0a65043562..faf1bc65f3 100755
--- a/bootstrap
+++ b/bootstrap
@@ -46,7 +46,7 @@ cmake_install_dest_default()
 
 cmake_toupper()
 {
-    echo "$1" | tr '[:lower:]' '[:upper:]'
+    echo "$1" | tr '[a-z]' '[A-Z]'
 }
 
 # Detect system and directory information.