diff --git a/player/command.c b/player/command.c
index 950d6dd80c..42938af140 100644
--- a/player/command.c
+++ b/player/command.c
@@ -2719,7 +2719,7 @@ static int mp_property_osd_w(void *ctx, struct m_property *prop,
                              int action, void *arg)
 {
     MPContext *mpctx = ctx;
-    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd, OSDTYPE_OSD);
+    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd);
     return m_property_int_ro(action, arg, vo_res.w);
 }
 
@@ -2727,7 +2727,7 @@ static int mp_property_osd_h(void *ctx, struct m_property *prop,
                              int action, void *arg)
 {
     MPContext *mpctx = ctx;
-    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd, OSDTYPE_OSD);
+    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd);
     return m_property_int_ro(action, arg, vo_res.h);
 }
 
@@ -2735,7 +2735,7 @@ static int mp_property_osd_par(void *ctx, struct m_property *prop,
                                int action, void *arg)
 {
     MPContext *mpctx = ctx;
-    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd, OSDTYPE_OSD);
+    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd);
     return m_property_double_ro(action, arg, vo_res.display_par);
 }
 
diff --git a/player/lua.c b/player/lua.c
index 680577554c..84d7295640 100644
--- a/player/lua.c
+++ b/player/lua.c
@@ -978,7 +978,7 @@ static int script_set_osd_ass(lua_State *L)
 static int script_get_osd_size(lua_State *L)
 {
     struct MPContext *mpctx = get_mpctx(L);
-    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd, OSDTYPE_EXTERNAL);
+    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd);
     double aspect = 1.0 * vo_res.w / MPMAX(vo_res.h, 1) /
                     (vo_res.display_par ? vo_res.display_par : 1);
     lua_pushnumber(L, vo_res.w);
@@ -990,7 +990,7 @@ static int script_get_osd_size(lua_State *L)
 static int script_get_osd_margins(lua_State *L)
 {
     struct MPContext *mpctx = get_mpctx(L);
-    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd, OSDTYPE_EXTERNAL);
+    struct mp_osd_res vo_res = osd_get_vo_res(mpctx->osd);
     lua_pushnumber(L, vo_res.ml);
     lua_pushnumber(L, vo_res.mt);
     lua_pushnumber(L, vo_res.mr);
diff --git a/player/osd.c b/player/osd.c
index 2a09911ac7..1baf9fb45e 100644
--- a/player/osd.c
+++ b/player/osd.c
@@ -561,6 +561,6 @@ void update_osd_msg(struct MPContext *mpctx)
         text = talloc_asprintf_append(text, "%s%s", text ? "\n" : "",
                                       mpctx->osd_msg_text);
     }
-    osd_set_text(osd, OSDTYPE_OSD, text);
+    osd_set_text(osd, text);
     talloc_free(text);
 }
diff --git a/player/sub.c b/player/sub.c
index 69c1dbbd19..6d01e0ca5d 100644
--- a/player/sub.c
+++ b/player/sub.c
@@ -71,8 +71,7 @@ void uninit_sub(struct MPContext *mpctx, struct track *track)
         reset_subtitles(mpctx, track);
         sub_select(track->d_sub, false);
         int order = get_order(mpctx, track);
-        if (order >= 0 && order <= 1)
-            osd_set_sub(mpctx->osd, OSDTYPE_SUB + order, NULL);
+        osd_set_sub(mpctx->osd, order, NULL);
     }
 }
 
@@ -182,8 +181,7 @@ void reinit_sub(struct MPContext *mpctx, struct track *track)
 
     sub_select(track->d_sub, true);
     int order = get_order(mpctx, track);
-    if (order >= 0 && order <= 1)
-        osd_set_sub(mpctx->osd, OSDTYPE_SUB + order, track->d_sub);
+    osd_set_sub(mpctx->osd, order, track->d_sub);
     sub_control(track->d_sub, SD_CTRL_SET_TOP, &(bool){!!order});
 }
 
diff --git a/sub/osd.c b/sub/osd.c
index c05fc5a0e3..e37b6cf106 100644
--- a/sub/osd.c
+++ b/sub/osd.c
@@ -109,6 +109,8 @@ static bool osd_res_equals(struct mp_osd_res a, struct mp_osd_res b)
 
 struct osd_state *osd_create(struct mpv_global *global)
 {
+    assert(MAX_OSD_PARTS >= OSDTYPE_COUNT);
+
     struct osd_state *osd = talloc_zero(NULL, struct osd_state);
     *osd = (struct osd_state) {
         .opts = global->opts,
@@ -151,24 +153,25 @@ void osd_changed_unlocked(struct osd_state *osd, int obj)
     osd->want_redraw = true;
 }
 
-void osd_set_text(struct osd_state *osd, int obj, const char *text)
+void osd_set_text(struct osd_state *osd, const char *text)
 {
     pthread_mutex_lock(&osd->lock);
-    struct osd_object *osd_obj = osd->objs[obj];
+    struct osd_object *osd_obj = osd->objs[OSDTYPE_OSD];
     if (!text)
         text = "";
     if (strcmp(osd_obj->text, text) != 0) {
         talloc_free(osd_obj->text);
         osd_obj->text = talloc_strdup(osd_obj, text);
-        osd_changed_unlocked(osd, obj);
+        osd_changed_unlocked(osd, osd_obj->type);
     }
     pthread_mutex_unlock(&osd->lock);
 }
 
-void osd_set_sub(struct osd_state *osd, int obj, struct dec_sub *dec_sub)
+void osd_set_sub(struct osd_state *osd, int index, struct dec_sub *dec_sub)
 {
     pthread_mutex_lock(&osd->lock);
-    osd->objs[obj]->sub = dec_sub;
+    if (index >= 0 && index < 2)
+        osd->objs[OSDTYPE_SUB + index]->sub = dec_sub;
     pthread_mutex_unlock(&osd->lock);
 }
 
@@ -405,10 +408,11 @@ bool osd_query_and_reset_want_redraw(struct osd_state *osd)
     return r;
 }
 
-struct mp_osd_res osd_get_vo_res(struct osd_state *osd, int obj)
+struct mp_osd_res osd_get_vo_res(struct osd_state *osd)
 {
     pthread_mutex_lock(&osd->lock);
-    struct mp_osd_res res = osd->objs[obj]->vo_res;
+    // Any OSDTYPE is fine; but it mustn't be a subtitle one (can have lower res.)
+    struct mp_osd_res res = osd->objs[OSDTYPE_OSD]->vo_res;
     pthread_mutex_unlock(&osd->lock);
     return res;
 }
diff --git a/sub/osd.h b/sub/osd.h
index 654330f152..494b534d5e 100644
--- a/sub/osd.h
+++ b/sub/osd.h
@@ -78,17 +78,8 @@ struct mp_osd_res {
     double display_par;
 };
 
-enum mp_osdtype {
-    OSDTYPE_SUB,
-    OSDTYPE_SUB2, // IDs must be numerically successive
-
-    OSDTYPE_OSD,
-
-    OSDTYPE_EXTERNAL,
-    OSDTYPE_EXTERNAL2,
-
-    MAX_OSD_PARTS
-};
+// 0 <= sub_bitmaps.render_index < MAX_OSD_PARTS
+#define MAX_OSD_PARTS 5
 
 // Start of OSD symbols in osd_font.pfb
 #define OSD_CODEPOINTS 0xE000
@@ -149,8 +140,8 @@ void osd_free(struct osd_state *osd);
 
 bool osd_query_and_reset_want_redraw(struct osd_state *osd);
 
-void osd_set_text(struct osd_state *osd, int obj, const char *text);
-void osd_set_sub(struct osd_state *osd, int obj, struct dec_sub *dec_sub);
+void osd_set_text(struct osd_state *osd, const char *text);
+void osd_set_sub(struct osd_state *osd, int index, struct dec_sub *dec_sub);
 
 bool osd_get_render_subs_in_filter(struct osd_state *osd);
 void osd_set_render_subs_in_filter(struct osd_state *osd, bool s);
@@ -188,7 +179,7 @@ void osd_draw_on_image_p(struct osd_state *osd, struct mp_osd_res res,
 struct mp_image_params;
 struct mp_osd_res osd_res_from_image_params(const struct mp_image_params *p);
 
-struct mp_osd_res osd_get_vo_res(struct osd_state *osd, int obj);
+struct mp_osd_res osd_get_vo_res(struct osd_state *osd);
 
 void osd_rescale_bitmaps(struct sub_bitmaps *imgs, int frame_w, int frame_h,
                          struct mp_osd_res res, double compensate_par);
diff --git a/sub/osd_state.h b/sub/osd_state.h
index c52c3354cd..0fff668d2d 100644
--- a/sub/osd_state.h
+++ b/sub/osd_state.h
@@ -7,6 +7,18 @@
 
 #define OSD_CONV_CACHE_MAX 4
 
+enum mp_osdtype {
+    OSDTYPE_SUB,
+    OSDTYPE_SUB2, // IDs must be numerically successive
+
+    OSDTYPE_OSD,
+
+    OSDTYPE_EXTERNAL,
+    OSDTYPE_EXTERNAL2,
+
+    OSDTYPE_COUNT
+};
+
 struct ass_state {
     struct mp_log *log;
     struct ass_track *track;