diff --git a/src/daemon/old_main.c b/src/daemon/old_main.c
index ab7a87f..e094107 100644
--- a/src/daemon/old_main.c
+++ b/src/daemon/old_main.c
@@ -39,7 +39,7 @@
 #endif
 
 
-int old_main()
+int old_main(void)
 {
    int ctlfd, newfd;
    struct sockaddr_un ctladdr;
diff --git a/src/headers/daemon.h b/src/headers/daemon.h
index 24a1a97..3ee77c4 100644
--- a/src/headers/daemon.h
+++ b/src/headers/daemon.h
@@ -204,7 +204,7 @@ void  gpm_exited(void);
 void  gpm_killed(int signo);
 
 int   open_console(const int mode);
-int old_main();
+int old_main(void);
 
 int processConn(int fd);
 int processMouse(int fd, Gpm_Event *event, Gpm_Type *type, int kd_mode);
@@ -234,7 +234,7 @@ void check_uniqueness(void);
 void check_kill(void);
 
 /* gpm.c */
-int old_main();
+int old_main(void);
 
 
 #endif
diff --git a/src/headers/gpm.h b/src/headers/gpm.h
index fe52e53..fa4b2a9 100644
--- a/src/headers/gpm.h
+++ b/src/headers/gpm.h
@@ -268,7 +268,10 @@ Gpm_Roi * Gpm_LowerRoi(Gpm_Roi *which, Gpm_Roi *after);
 /* libcurses.c */
 /* #include <curses.h>  Hmm... seems risky */
 
-extern int Gpm_Wgetch();
+/* Forward-declare ncurses WINDOW type for C23 compatibility.
+ * In C23, empty () means (void), so we need a proper prototype. */
+struct _win_st;
+extern int Gpm_Wgetch(struct _win_st *);
 #define Gpm_Getch() (Gpm_Wgetch(NULL))
 
 /* libxtra.c */
diff --git a/src/lib/libcurses.c b/src/lib/libcurses.c
index e7ebf84..33cca70 100644
--- a/src/lib/libcurses.c
+++ b/src/lib/libcurses.c
@@ -95,7 +95,7 @@ static Gpm_Event ev;
 /* JD patch 11/08/1998 */
 #define MAXNBPREVCHAR 4         /* I don't think more is usefull, JD */
     static int nbprevchar=0, prevchar[MAXNBPREVCHAR];
-    extern int gpm_convert_event(char *data, Gpm_Event *event);
+    extern int gpm_convert_event(unsigned char *data, Gpm_Event *event);
     int c; unsigned char mdata[4];
 
 /* JD patch 11/08/1998 */