diff --git a/Source/Preprocessor/cpp.c b/Source/Preprocessor/cpp.c
index 4366a8434..7e45c5bd4 100644
--- a/Source/Preprocessor/cpp.c
+++ b/Source/Preprocessor/cpp.c
@@ -1870,7 +1870,7 @@ String *Preprocessor_parse(String *s) {
 		push_imported();
 	      }
 	      dirname = Swig_file_dirname(Swig_last_file());
-	      if (sysfile || !strlen(dirname)) {
+	      if (sysfile || !Len(dirname)) {
 		Delete(dirname);
 		dirname = 0;
 	      }