diff --git a/src/library_sdl.js b/src/library_sdl.js
index 48e7bafaadaac..a0a0edb4c6c19 100644
--- a/src/library_sdl.js
+++ b/src/library_sdl.js
@@ -823,13 +823,16 @@ var LibrarySDL = {
 
     lookupKeyCodeForEvent(event) {
       var code = event.keyCode;
-      if (code >= 65 && code <= 90) {
+      if (code >= 65 && code <= 90) { // ASCII A-Z
         code += 32; // make lowercase for SDL
       } else {
+        // Look up DOM code in the keyCodes table with fallback for ASCII codes
+        // which can match between DOM codes and SDL keycodes (allows keyCodes
+        // to be smaller).
+        code = SDL.keyCodes[code] || (code < 128 ? code : 0);
 #if RUNTIME_DEBUG
-        if (!(event.keyCode in SDL.keyCodes)) dbg('unknown keyCode: ', event.keyCode);
+        if (!code) dbg('unmapped keyCode: ', event.keyCode);
 #endif
-        code = SDL.keyCodes[event.keyCode] || event.keyCode;
         // If this is one of the modifier keys (224 | 1<<10 - 227 | 1<<10), and the event specifies that it is
         // a right key, add 4 to get the right key SDL key code.
         if (event.location === 2 /*KeyboardEvent.DOM_KEY_LOCATION_RIGHT*/ && code >= (224 | 1<<10) && code <= (227 | 1<<10)) {
@@ -854,6 +857,8 @@ var LibrarySDL = {
         case 'keyup': {
           var down = event.type === 'keydown';
           var code = SDL.lookupKeyCodeForEvent(event);
+          // Ignore key events that we don't (yet) map to SDL keys
+          if (!code) return;
 #if !SAFE_HEAP
           // Assigning a boolean to HEAP8, that's alright but Closure would like to warn about it.
           // TODO(https://github.com/emscripten-core/emscripten/issues/16311):
@@ -938,6 +943,8 @@ var LibrarySDL = {
           dbg(`received ${event.type} event: keyCode=${event.keyCode}, key=${event.key}, code=${event.code}`);
 #endif
           var key = SDL.lookupKeyCodeForEvent(event);
+          // Ignore key events that we don't (yet) map to SDL keys
+          if (!key) return false;
           var scan;
           if (key >= 1024) {
             scan = key - 1024;
diff --git a/test/browser/test_sdl_key.c b/test/browser/test_sdl_key.c
index 4f7dbfe898a1a..00cbb4493e465 100644
--- a/test/browser/test_sdl_key.c
+++ b/test/browser/test_sdl_key.c
@@ -72,8 +72,8 @@ int main(int argc, char **argv) {
 
   emscripten_set_main_loop(one, 0, 0);
 
-  EM_ASM({keydown(1250);keydown(38);keyup(38);keyup(1250);}); // alt, up
-  EM_ASM({keydown(1248);keydown(1249);keydown(40);keyup(40);keyup(1249);keyup(1248);}); // ctrl, shift, down
+  EM_ASM({keydown(18);keydown(38);keyup(38);keyup(18);}); // alt, up
+  EM_ASM({keydown(17);keydown(16);keydown(40);keyup(40);keyup(16);keyup(17);}); // ctrl, shift, down
   EM_ASM({keydown(37);keyup(37);}); // left
   EM_ASM({keydown(39);keyup(39);}); // right
 
diff --git a/test/test_browser.py b/test/test_browser.py
index 4bc9e57e8f3e2..0b568a6ac352c 100644
--- a/test/test_browser.py
+++ b/test/test_browser.py
@@ -990,8 +990,8 @@ def post():
       html = html.replace('</body>', '''
 <script src='fake_events.js'></script>
 <script>
-simulateKeyDown(1250);simulateKeyDown(38);simulateKeyUp(38);simulateKeyUp(1250); // alt, up
-simulateKeyDown(1248);simulateKeyDown(1249);simulateKeyDown(40);simulateKeyUp(40);simulateKeyUp(1249);simulateKeyUp(1248); // ctrl, shift, down
+simulateKeyDown(18);simulateKeyDown(38);simulateKeyUp(38);simulateKeyUp(18); // alt, up
+simulateKeyDown(17);simulateKeyDown(16);simulateKeyDown(40);simulateKeyUp(40);simulateKeyUp(16);simulateKeyUp(17); // ctrl, shift, down
 simulateKeyDown(37);simulateKeyUp(37); // left
 simulateKeyDown(39);simulateKeyUp(39); // right
 simulateKeyDown(65);simulateKeyUp(65); // a