diff --git a/lib/system_win32.h b/lib/system_win32.h
index 95f4af8a7..c07cf1fb7 100644
--- a/lib/system_win32.h
+++ b/lib/system_win32.h
@@ -49,7 +49,7 @@ typedef enum {
 } PlatformIdentifier;
 
 /* We use our own typedef here since some headers might lack this */
-typedef unsigned int(WINAPI *IF_NAMETOINDEX_FN)(char *);
+typedef unsigned int(WINAPI *IF_NAMETOINDEX_FN)(const char *);
 
 /* This is used instread of if_nametoindex if available on Windows */
 IF_NAMETOINDEX_FN Curl_if_nametoindex;