diff --git a/kitty/key_encoding.c b/kitty/key_encoding.c
index a7c7bf1e2..3db059734 100644
--- a/kitty/key_encoding.c
+++ b/kitty/key_encoding.c
@@ -307,6 +307,7 @@ is_legacy_ascii_key(uint32_t key) {
         case ',':
         case '.':
         case '/':
+        case ' ':
             return true;
         default:
             return false;
diff --git a/kitty_tests/keys.py b/kitty_tests/keys.py
index cbc044ab7..bc01cfc8c 100644
--- a/kitty_tests/keys.py
+++ b/kitty_tests/keys.py
@@ -394,6 +394,7 @@ class TestKeys(BaseTest):
         ae(enc(key=ord(':'), shifted_key=ord('/'), mods=shift | alt), '\x1b/')
         ae(enc(key=ord(' ')), ' ')
         ae(enc(key=ord(' '), mods=ctrl), '\0')
+        ae(enc(key=ord(' '), mods=alt), '\x1b ')
         ae(enc(key=ord('i'), mods=ctrl | shift), csi(ctrl | shift, ord('i')))
         ae(enc(key=defines.GLFW_FKEY_LEFT_SHIFT), '')
         ae(enc(key=defines.GLFW_FKEY_CAPS_LOCK), '')