diff --git a/lib/hook.sh b/lib/hook.sh
index f1b79df..4b8d86a 100644
--- a/lib/hook.sh
+++ b/lib/hook.sh
@@ -120,7 +120,7 @@ _Dbg_debug_trap_handler() {
     _Dbg_save_args "$@"
 
     typeset _Dbg_full_filename
-    _Dbg_full_filename=$(_Dbg_is_file "${BASH_SOURCE[1]}")
+    _Dbg_full_filename="$(_Dbg_is_file "${BASH_SOURCE[1]}")"
     if [[ -r "$_Dbg_full_filename" ]] ; then
 	_Dbg_file2canonic["${BASH_SOURCE[1]}"]="$_Dbg_full_filename"
     fi