diff --git a/Makefile.emscripten b/Makefile.emscripten
index b1019f4..864943e 100644
--- a/Makefile.emscripten
+++ b/Makefile.emscripten
@@ -13,8 +13,9 @@ EMFLAGS += -s NO_EXIT_RUNTIME=1
 LFLAGS := $(EMFLAGS)
 LFLAGS += -s EXPORTED_FUNCTIONS="['_main','_ags_setAntialiasedStringMode', '_ald_getdata', '_ald_freedata', '_sjis2unicode']"
 LFLAGS += -s EXTRA_EXPORTED_RUNTIME_METHODS="['getValue','getMemory','addRunDependency','removeRunDependency']"
+LFLAGS += --js-library emscripten/library.js
 
-SYNCLIST := -s EMTERPRETIFY_SYNCLIST="['_muspcm_load_no','_muspcm_load_mixlr']"
+SYNCLIST := -s EMTERPRETIFY_SYNCLIST="['_muspcm_load_no','_muspcm_load_mixlr','_wait_vsync']"
 
 WASMFLAGS := -s WASM=1 -s "BINARYEN_TRAP_MODE='allow'"
 ASMJSFLAGS :=
diff --git a/emscripten/library.js b/emscripten/library.js
new file mode 100644
index 0000000..fbf5dda
--- /dev/null
+++ b/emscripten/library.js
@@ -0,0 +1,10 @@
+mergeInto(LibraryManager.library, {
+	wait_vsync: function() {
+		EmterpreterAsync.handle(function(resume) {
+			window.requestAnimationFrame(function() {
+				if (ABORT) return; // do this manually; we can't call into Browser.safeSetTimeout, because that is paused/resumed!
+				resume();
+			});
+		});
+	}
+});
diff --git a/emterpretify_whitelist b/emterpretify_whitelist
index 85ba630..841cfe3 100644
--- a/emterpretify_whitelist
+++ b/emterpretify_whitelist
@@ -1 +1 @@
-  -s EMTERPRETIFY_WHITELIST='["_ags_eCopyArea", "_ags_fadeIn", "_ags_fadeOut", "_ags_fader", "_ags_whiteIn", "_ags_whiteOut", "_checkMessage", "_check_command", "_commandCD", "_commandCE", "_commandH", "_commandHH", "_commandIK", "_commandMP", "_commandPF", "_commandPW", "_commandSM", "_commandSP", "_commandSQ", "_commandVA", "_commandY", "_commandZT20", "_commandZT21", "_commands2F1E", "_commands2F21", "_commands2F7C", "_commands2F7D", "_commands2F7E", "_commands2F7F", "_eCopyArea1", "_eCopyArea11", "_eCopyArea12", "_eCopyArea13", "_eCopyArea14", "_eCopyArea15", "_eCopyArea16", "_eCopyArea17", "_eCopyArea18", "_eCopyArea19", "_eCopyArea2", "_eCopyArea20", "_eCopyArea21", "_eCopyArea22", "_eCopyArea23", "_eCopyArea24", "_eCopyArea25", "_eCopyArea26", "_eCopyArea3", "_eCopyArea33", "_eCopyArea34", "_eCopyArea39", "_eCopyArea4", "_eCopyArea40", "_eCopyArea48", "_eCopyArea49", "_eCopyArea5", "_eCopyArea5sp", "_eCopyArea6", "_eCopyArea7", "_eCopyArea8", "_eCopyArea9", "_main", "_msg_putMessage", "_mus_pcm_load", "_mus_pcm_mix", "_mus_pcm_start", "_nact_main", "_sdl_keywait", "_sdl_sleep", "_sel_select", "_sys_addMsg", "_sys_hit_any_key", "_sys_key_releasewait"]'
+  -s EMTERPRETIFY_WHITELIST='["_ags_eCopyArea", "_ags_fadeIn", "_ags_fadeOut", "_ags_fader", "_ags_whiteIn", "_ags_whiteOut", "_checkMessage", "_check_command", "_commandCD", "_commandCE", "_commandH", "_commandHH", "_commandIK", "_commandMP", "_commandPF", "_commandPW", "_commandSM", "_commandSP", "_commandSQ", "_commandVA", "_commandY", "_commandZT20", "_commandZT21", "_commands2F1E", "_commands2F21", "_commands2F7C", "_commands2F7D", "_commands2F7E", "_commands2F7F", "_eCopyArea1", "_eCopyArea11", "_eCopyArea12", "_eCopyArea13", "_eCopyArea14", "_eCopyArea15", "_eCopyArea16", "_eCopyArea17", "_eCopyArea18", "_eCopyArea19", "_eCopyArea2", "_eCopyArea20", "_eCopyArea21", "_eCopyArea22", "_eCopyArea23", "_eCopyArea24", "_eCopyArea25", "_eCopyArea26", "_eCopyArea3", "_eCopyArea33", "_eCopyArea34", "_eCopyArea39", "_eCopyArea4", "_eCopyArea40", "_eCopyArea48", "_eCopyArea49", "_eCopyArea5", "_eCopyArea5sp", "_eCopyArea6", "_eCopyArea7", "_eCopyArea8", "_eCopyArea9", "_main", "_msg_putMessage", "_mus_pcm_load", "_mus_pcm_mix", "_mus_pcm_start", "_nact_main", "_sdl_keywait", "_sdl_sleep", "_sdl_wait_vsync", "_sel_select", "_sys_addMsg", "_sys_hit_any_key", "_sys_key_releasewait"]'
diff --git a/src/nact.c b/src/nact.c
index cfa4b4f..63de06f 100644
--- a/src/nact.c
+++ b/src/nact.c
@@ -225,15 +225,13 @@ void nact_main() {
 		if (cdrom_getpos_count >= 2) {
 			if (!nact->is_message_locked && nact->input_state == InputNotChecked)
 				sys_getInputInfo();
-			sdl_updateScreen();
-			Sleep(10);
+			WaitVsync();
 			cdrom_getpos_count = 0;
 		}
 #endif
 #ifdef ENABLE_SDL
 		if (nact->input_state == InputCheckMissed) {
-			sdl_updateScreen();
-			Sleep(10);
+			WaitVsync();
 		}
 #endif
 	}
diff --git a/src/sdl_core.h b/src/sdl_core.h
index d4b8a01..b91f1a1 100644
--- a/src/sdl_core.h
+++ b/src/sdl_core.h
@@ -101,6 +101,7 @@ extern void sdl_setAutoRepeat(boolean bool);
 extern void sdl_mainIteration();
 extern boolean RawKeyInfo[];
 extern void sdl_sleep(int msec);
+extern void sdl_wait_vsync();
 extern void sdl_sync();
 
 /* 初期化関係 */
@@ -172,5 +173,11 @@ extern void sdl_sync();
 #define ResourceInit(c,v) sdl_ResourceInit((c),(v))
 #define SetNoShmMode() /* NO */
 #define Sleep(ms) sdl_sleep(ms)
+#define WaitVsync() sdl_wait_vsync()
+
+#ifdef __EMSCRIPTEN__
+// library.js
+void wait_vsync(void);
+#endif
 
 #endif /* !__SDL_CORE__ */
diff --git a/src/sdl_draw.c b/src/sdl_draw.c
index 1d00d10..2fc41e2 100644
--- a/src/sdl_draw.c
+++ b/src/sdl_draw.c
@@ -84,6 +84,15 @@ void sdl_sleep(int msec) {
 #endif
 }
 
+void sdl_wait_vsync() {
+	sdl_updateScreen();
+#ifdef __EMSCRIPTEN__
+	wait_vsync();
+#else
+	SDL_Delay(16);
+#endif
+}
+
 /* off-screen の指定領域を Main Window へ転送 */
 void sdl_updateArea(MyRectangle *src, MyPoint *dst) {
 	SDL_Rect rect_s, rect_d;
diff --git a/src/sdl_event.c b/src/sdl_event.c
index c72b610..74eb9f0 100644
--- a/src/sdl_event.c
+++ b/src/sdl_event.c
@@ -22,6 +22,7 @@
 
 #include "config.h"
 
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -195,10 +196,13 @@ static void sdl_getEvent(void) {
 
 int sdl_keywait(int msec, boolean cancel) {
 	int key=0, n;
-	int end = get_high_counter(SYSTEMCOUNTER_MSEC) + msec;
+	int end = msec == INT_MAX ? INT_MAX : get_high_counter(SYSTEMCOUNTER_MSEC) + msec;
 	
 	while ((n = end - get_high_counter(SYSTEMCOUNTER_MSEC)) > 0) {
-		sdl_sleep(n < 16 ? n : 16);
+		if (n <= 16)
+			sdl_sleep(n);
+		else
+			sdl_wait_vsync();
 		nact->callback();
 		sdl_getEvent();
 		key = check_button() | sdl_getKeyInfo() | joy_getinfo();
diff --git a/src/xcore.h b/src/xcore.h
index 951664c..ea29d65 100644
--- a/src/xcore.h
+++ b/src/xcore.h
@@ -168,5 +168,6 @@ extern boolean   RawKeyInfo[256];
 // #define MainIteration() Xcore_mainIteration()
 #define EventCallback Xcore_eventCallback
 #define Sleep(ms) usleep((ms) * 1000)
+#define WaitVsync() Sleep(16)
 
 #endif /* !__XCORE_H__ */