diff --git a/src/include/86box/unix_sdl.h b/src/include/86box/unix_sdl.h
index 0054ed938..27d7ec0aa 100644
--- a/src/include/86box/unix_sdl.h
+++ b/src/include/86box/unix_sdl.h
@@ -2,9 +2,9 @@
 #define _UNIX_SDL_H
 
 extern void sdl_close(void);
-extern int  sdl_inits();
-extern int  sdl_inith();
-extern int  sdl_initho();
+extern int  sdl_inits(void);
+extern int  sdl_inith(void);
+extern int  sdl_initho(void);
 extern int  sdl_pause(void);
 extern void sdl_resize(int x, int y);
 extern void sdl_enable(int enable);
diff --git a/src/unix/macOSXGlue.h b/src/unix/macOSXGlue.h
index f49402805..44bf9e7f6 100644
--- a/src/unix/macOSXGlue.h
+++ b/src/unix/macOSXGlue.h
@@ -14,7 +14,7 @@
 CF_IMPLICIT_BRIDGING_ENABLED
 CF_EXTERN_C_BEGIN
 void getDefaultROMPath(char *);
-int  toto();
+int  toto(void);
 
 CF_EXTERN_C_END
 CF_IMPLICIT_BRIDGING_DISABLED
diff --git a/src/unix/unix.c b/src/unix/unix.c
index 4410118f3..296da5e14 100644
--- a/src/unix/unix.c
+++ b/src/unix/unix.c
@@ -468,12 +468,12 @@ ui_sb_update_tip(int arg)
 }
 
 void
-ui_sb_update_panes()
+ui_sb_update_panes(void)
 {
 }
 
 void
-ui_sb_update_text()
+ui_sb_update_text(void)
 {
 }
 
@@ -699,7 +699,7 @@ typedef struct mouseinputdata {
 SDL_mutex            *mousemutex;
 static mouseinputdata mousedata;
 void
-mouse_poll()
+mouse_poll(void)
 {
     SDL_LockMutex(mousemutex);
     mouse_x          = mousedata.deltax;
@@ -754,7 +754,7 @@ plat_pause(int p)
 }
 
 void
-plat_init_rom_paths()
+plat_init_rom_paths(void)
 {
 #ifndef __APPLE__
     if (getenv("XDG_DATA_HOME")) {
@@ -1202,7 +1202,7 @@ main(int argc, char **argv)
                 case SDL_RENDER_DEVICE_RESET:
                 case SDL_RENDER_TARGETS_RESET:
                     {
-                        extern void sdl_reinit_texture();
+                        extern void sdl_reinit_texture(void);
                         sdl_reinit_texture();
                         break;
                     }
@@ -1238,7 +1238,7 @@ main(int argc, char **argv)
             sdl_blit(params.x, params.y, params.w, params.h);
         }
         if (title_set) {
-            extern void ui_window_title_real();
+            extern void ui_window_title_real(void);
             ui_window_title_real();
         }
         if (video_fullscreen && keyboard_isfsexit()) {
@@ -1303,13 +1303,13 @@ joystick_process(void)
 {
 }
 void
-startblit()
+startblit(void)
 {
     SDL_LockMutex(blitmtx);
 }
 
 void
-endblit()
+endblit(void)
 {
     SDL_UnlockMutex(blitmtx);
 }
diff --git a/src/unix/unix_sdl.c b/src/unix/unix_sdl.c
index bd2f3937b..bc89c9290 100644
--- a/src/unix/unix_sdl.c
+++ b/src/unix/unix_sdl.c
@@ -46,7 +46,7 @@ double              mouse_sensitivity = 1.0;                  /* Unused. */
 double              mouse_x_error = 0.0, mouse_y_error = 0.0; /* Unused. */
 static uint8_t      interpixels[17842176];
 
-extern void RenderImGui();
+extern void RenderImGui(void);
 static void
 sdl_integer_scale(double *d, double *g)
 {
@@ -61,7 +61,7 @@ sdl_integer_scale(double *d, double *g)
     }
 }
 
-void sdl_reinit_texture();
+void sdl_reinit_texture(void);
 
 static void
 sdl_stretch(int *w, int *h, int *x, int *y)
@@ -141,7 +141,7 @@ sdl_blit_shim(int x, int y, int w, int h, int monitor_index)
     video_blit_complete_monitor(monitor_index);
 }
 
-void ui_window_title_real();
+void ui_window_title_real(void);
 
 void
 sdl_real_blit(SDL_Rect *r_src)
@@ -286,7 +286,7 @@ sdl_select_best_hw_driver(void)
 }
 
 void
-sdl_reinit_texture()
+sdl_reinit_texture(void)
 {
     sdl_destroy_texture();
 
@@ -416,19 +416,19 @@ sdl_init_common(int flags)
 }
 
 int
-sdl_inits()
+sdl_inits(void)
 {
     return sdl_init_common(0);
 }
 
 int
-sdl_inith()
+sdl_inith(void)
 {
     return sdl_init_common(RENDERER_HARDWARE);
 }
 
 int
-sdl_initho()
+sdl_initho(void)
 {
     return sdl_init_common(RENDERER_HARDWARE | RENDERER_OPENGL);
 }
@@ -462,7 +462,7 @@ wchar_t    sdl_win_title[512] = { L'8', L'6', L'B', L'o', L'x', 0 };
 SDL_mutex *titlemtx           = NULL;
 
 void
-ui_window_title_real()
+ui_window_title_real(void)
 {
     char *res;
     if (sizeof(wchar_t) == 1) {