diff --git a/c-programming/io/freadln.h b/c-programming/io/freadln.h
index eb3c78c..8680dc2 100644
--- a/c-programming/io/freadln.h
+++ b/c-programming/io/freadln.h
@@ -29,6 +29,6 @@ enum freadln_status {
     }                                                                         \
 } while (0)
 
-ssize_t freadln(char** output);
+ssize_t freadln(char** output, size_t* length_out);
 
 #endif /* _FREADLN_H */