diff --git a/in_sdl.c b/in_sdl.c
index a84c781..518e8cf 100644
--- a/in_sdl.c
+++ b/in_sdl.c
@@ -19,11 +19,18 @@
 typedef unsigned long keybits_t;
 #define KEYBITS_WORD_BITS (sizeof(keybits_t) * 8)
 
+enum mod_state {
+	MOD_NO,
+	MOD_MAYBE,
+	MOD_YES
+};
+
 struct in_sdl_state {
 	const in_drv_t *drv;
 	SDL_Joystick *joy;
 	int joy_id;
 	int axis_keydown[2];
+	enum mod_state mod_state;
 	keybits_t keystate[SDLK_LAST / KEYBITS_WORD_BITS + 1];
 	// emulator keys should always be processed immediately lest one is lost
 	keybits_t emu_keys[SDLK_LAST / KEYBITS_WORD_BITS + 1];
@@ -259,6 +266,97 @@ static int get_keystate(keybits_t *keystate, int sym)
 	return !!(*ks_word & mask);
 }
 
+static int translate_keystate(struct in_sdl_state *state, SDL_Event *event)
+{
+	const struct in_pdata *pdata = state->drv->pdata;
+	const struct mod_keymap *map;
+	SDL_Event new_event;
+	short key = (short)event->key.keysym.sym;
+	uint8_t type  = event->type;
+	short mod_key = pdata->mod_key;
+	int i;
+	int ret = 1;
+
+	if (!mod_key)
+		return 1;
+
+	if (state->mod_state == MOD_NO && key != mod_key)
+		return 1;
+
+	if (key == mod_key) {
+		if (type == SDL_KEYDOWN) {
+			/* Pressed mod, maybe a combo? Ignore the keypress
+			 * until it's determined */
+			state->mod_state = MOD_MAYBE;
+
+			for (i = 0; i < pdata->modmap_size; i++) {
+				map = &pdata->mod_keymap[i];
+
+				if (get_keystate(state->keystate, map->inkey)) {
+					state->mod_state = MOD_YES;
+					new_event.type = SDL_KEYUP;
+					new_event.key.state = SDL_RELEASED;
+					new_event.key.keysym.sym = map->inkey;
+					SDL_PushEvent(&new_event);
+
+					new_event.type = SDL_KEYDOWN;
+					new_event.key.state = SDL_PRESSED;
+					new_event.key.keysym.sym = map->outkey;
+					SDL_PushEvent(&new_event);
+				}
+			}
+
+			ret = -1;
+		} else if (state->mod_state == MOD_MAYBE) {
+			/* Released mod without combo, simulate down and up */
+			SDL_PushEvent(event);
+			state->mod_state = MOD_NO;
+			event->type = SDL_KEYDOWN;
+			ret = 1;
+		} else if (state->mod_state == MOD_YES) {
+			/* Released mod, switch all mod keys to unmod */
+			state->mod_state = MOD_NO;
+
+			for (i = 0; i < pdata->modmap_size; i++) {
+				map = &pdata->mod_keymap[i];
+
+				if (get_keystate(state->keystate, map->outkey)) {
+					state->mod_state = MOD_NO;
+					new_event.type = SDL_KEYUP;
+					new_event.key.state = SDL_RELEASED;
+					new_event.key.keysym.sym = map->outkey;
+					SDL_PushEvent(&new_event);
+
+					new_event.type = SDL_KEYDOWN;
+					new_event.key.state = SDL_PRESSED;
+					new_event.key.keysym.sym = map->inkey;
+					SDL_PushEvent(&new_event);
+				}
+			}
+			ret = -1;
+		}
+	} else {
+		for (i = 0; i < pdata->modmap_size; i++) {
+			map = &pdata->mod_keymap[i];
+
+			if (map->inkey == key) {
+				state->mod_state = MOD_YES;
+
+				/* Releasing the original key? Allow it through,
+				 * Otherwise, replace with modified key. */
+				if (!(event->type == SDL_KEYUP &&
+				      get_keystate(state->keystate, map->inkey)))
+					event->key.keysym.sym = map->outkey;
+
+				break;
+			}
+		}
+		ret = 1;
+	}
+
+	return ret;
+}
+
 static int handle_event(struct in_sdl_state *state, SDL_Event *event,
 	int *kc_out, int *down_out, int *emu_out)
 {
@@ -267,6 +365,9 @@ static int handle_event(struct in_sdl_state *state, SDL_Event *event,
 	if (event->type != SDL_KEYDOWN && event->type != SDL_KEYUP)
 		return -1;
 
+	if (translate_keystate(state, event) < 0)
+		return -1;
+
 	emu = get_keystate(state->emu_keys, event->key.keysym.sym);
 	update_keystate(state->keystate, event->key.keysym.sym,
 		event->type == SDL_KEYDOWN);
diff --git a/input.h b/input.h
index 360b65b..895ad61 100644
--- a/input.h
+++ b/input.h
@@ -110,6 +110,11 @@ struct menu_keymap {
 	short pbtn;
 };
 
+struct mod_keymap {
+	short inkey;
+	short outkey;
+};
+
 struct in_pdata {
 	const struct in_default_bind *defbinds;
 	const struct menu_keymap *key_map;
@@ -117,6 +122,9 @@ struct in_pdata {
 	const struct menu_keymap *joy_map;
 	size_t jmap_size;
 	const char * const *key_names;
+	short mod_key;
+	const struct mod_keymap *mod_keymap;
+	size_t modmap_size;
 };
 
 /* to be called by drivers */