diff --git a/config.h b/config.h
index 42e5498..2b0acc3 100644
--- a/config.h
+++ b/config.h
@@ -31,9 +31,9 @@
 // define parameters
 typedef struct _Settings
 {
-    char *input;
-    char *maskpoly;
-    char *output;
+    const char *input;
+    const char *maskpoly;
+    const char *output;
     int64_t window;
     int64_t depth;
     int64_t sizepoly;