diff --git a/kitty/launch.py b/kitty/launch.py
index c909c3794..f3927e105 100644
--- a/kitty/launch.py
+++ b/kitty/launch.py
@@ -620,7 +620,7 @@ def _launch(
                 new_window.overlay_type = OverlayType.main
             if opts.var:
                 for key, val in parse_var(opts.var):
-                    new_window.user_vars[key] = val
+                    new_window.set_user_var(key, val)
             return new_window
     return None
 
diff --git a/kitty/rc/set_user_vars.py b/kitty/rc/set_user_vars.py
index 712e3a1ca..deb9296f2 100644
--- a/kitty/rc/set_user_vars.py
+++ b/kitty/rc/set_user_vars.py
@@ -30,21 +30,19 @@ class SetUserVars(RemoteCommand):
         return {'match': opts.match, 'var': args, 'self': True}
 
     def response_from_kitty(self, boss: Boss, window: Optional[Window], payload_get: PayloadGetType) -> ResponseType:
-        remove = set()
         val = {}
         for x in payload_get('var') or ():
             a, sep, b = x.partition('=')
             if sep:
                 val[a] = b
             else:
-                remove.add(a)
+                val[a] = None
         lines = []
         for window in self.windows_for_match_payload(boss, window, payload_get):
             if window:
-                if val or remove:
-                    window.user_vars.update(val)
-                    for x in remove:
-                        window.user_vars.pop(x, None)
+                if val:
+                    for k, v in val.items():
+                        window.set_user_var(k, v)
                 else:
                     lines.append('\n'.join(f'{k}={v}' for k, v in window.user_vars.items()))
         return '\n\n'.join(lines)
diff --git a/kitty/window.py b/kitty/window.py
index 3e1d70c90..e9c924409 100644
--- a/kitty/window.py
+++ b/kitty/window.py
@@ -100,6 +100,7 @@ from .utils import (
     path_from_osc7_url,
     resolve_custom_file,
     resolved_shell,
+    sanitize_control_codes,
     sanitize_for_bracketed_paste,
     sanitize_title,
     sanitize_url_for_dispay_to_user,
@@ -850,13 +851,16 @@ class Window:
         self.override_title = title or None
         self.title_updated()
 
-    def set_user_var(self, key: str, val: Optional[bytes]) -> None:
+    def set_user_var(self, key: str, val: Optional[Union[str, bytes]]) -> None:
+        key = sanitize_control_codes(key).replace('\n', ' ')
         self.user_vars.pop(key, None)  # ensure key will be newest in user_vars even if already present
         if len(self.user_vars) > 64:  # dont store too many user vars
             oldest_key = next(iter(self.user_vars))
             self.user_vars.pop(oldest_key)
         if val is not None:
-            self.user_vars[key] = val.decode('utf-8', 'replace')
+            if isinstance(val, bytes):
+                val = val.decode('utf-8', 'replace')
+            self.user_vars[key] = sanitize_control_codes(val).replace('\n', ' ')
 
     # screen callbacks {{{