diff --git a/docs/changelog.rst b/docs/changelog.rst
index 21d1e6674..47a083e59 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -40,6 +40,8 @@ Detailed list of changes
 
 - Text rendering: Use sRGB correct linear gamma blending for nicer font rendering and better color accuracy with transparent windows. See the option :opt:`text_composition_strategy` for details. (:pull:`5969`)
 
+- Fix a regression in 0.27.0 that broke kitty @ set-font-size 0 (:iss:`5992`)
+
 
 0.27.1 [2023-02-07]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/kitty/rc/set_font_size.py b/kitty/rc/set_font_size.py
index ecfd8c723..5d14a65ec 100644
--- a/kitty/rc/set_font_size.py
+++ b/kitty/rc/set_font_size.py
@@ -11,7 +11,7 @@ if TYPE_CHECKING:
 
 class SetFontSize(RemoteCommand):
     protocol_spec = __doc__ = '''
-    size+/float: The new font size in pts (a positive number)
+    size+/float: The new font size in pts (a positive number). If absent is assumed to be zero which means reset to default.
     all/bool: Boolean whether to change font size in the current window or all windows
     increment_op/choices.+.-: The string ``+`` or ``-`` to interpret size as an increment
     '''
@@ -45,7 +45,7 @@ the font size for any newly created OS Windows in the future.
     def response_from_kitty(self, boss: Boss, window: Optional[Window], payload_get: PayloadGetType) -> ResponseType:
         boss.change_font_size(
             payload_get('all'),
-            payload_get('increment_op'), payload_get('size'))
+            payload_get('increment_op'), payload_get('size') or 0)
         return None