diff --git a/shiny/ui/_layout_columns.py b/shiny/ui/_layout_columns.py
index 77e551a8d..7bd2394db 100644
--- a/shiny/ui/_layout_columns.py
+++ b/shiny/ui/_layout_columns.py
@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from enum import Enum
-from typing import Dict, Iterable, Optional, TypeVar, Union, cast
+from typing import Dict, Iterable, Literal, Optional, Tuple, TypeVar, Union, cast
 from warnings import warn
 
 from htmltools import Tag, TagAttrs, TagAttrValue, TagChild, css
@@ -15,24 +15,20 @@
 T = TypeVar("T")
 
 
-class Breakpoints(Enum):
-    """
-    References
-    ----------
-    * [Available Bootstrap breakpoints](https://getbootstrap.com/docs/5.3/layout/breakpoints/#available-breakpoints)
-    """
+Breakpoint = Literal["xs", "sm", "md", "lg", "xl", "xxl"]
+"""
+References
+----------
+* [Available Bootstrap breakpoints](https://getbootstrap.com/docs/5.3/layout/breakpoints/#available-breakpoints)
+"""
+
 
-    xs = "xs"
-    sm = "sm"
-    md = "md"
-    lg = "lg"
-    xl = "xl"
-    xxl = "xxl"
+breakpoints: Tuple[Breakpoint, ...] = ("xs", "sm", "md", "lg", "xl", "xxl")
 
 
-BreakpointsSoft = Dict[Breakpoints, Union[Iterable[T], T, None]]
-BreakpointsOptional = Dict[Breakpoints, Union[Iterable[T], None]]
-BreakpointsComplete = Dict[Breakpoints, Iterable[T]]
+BreakpointsSoft = Dict[Breakpoint, Union[Iterable[T], T, None]]
+BreakpointsOptional = Dict[Breakpoint, Union[Iterable[T], None]]
+BreakpointsComplete = Dict[Breakpoint, Iterable[T]]
 BreakpointsUser = Union[BreakpointsSoft[T], Iterable[T], T, None]
 
 
@@ -155,16 +151,15 @@ def as_col_spec(
         return None
 
     if not isinstance(col_widths, Dict):
-        return {Breakpoints.md: validate_col_width(col_widths, n_kids, Breakpoints.md)}
+        return {"md": validate_col_width(col_widths, n_kids, "md")}
 
     ret: BreakpointsOptional[int] = {}
     col_widths_items = cast(BreakpointsSoft[int], col_widths).items()
 
     for brk, value in col_widths_items:
-        bs_breakpoints = [str(bp.value) for bp in Breakpoints]
-        if str(brk) not in bs_breakpoints:
+        if brk not in breakpoints:
             raise ValueError(
-                f"Breakpoint '{brk}' is not valid. Valid breakpoints are: {', '.join(bs_breakpoints)}'."
+                f"Breakpoint '{brk}' is not valid. Valid breakpoints are: {', '.join(breakpoints)}'."
             )
 
         if value is None:
@@ -180,7 +175,7 @@ def as_col_spec(
 
 
 def validate_col_width(
-    x: Iterable[int] | int, n_kids: int, break_name: Breakpoints
+    x: Iterable[int] | int, n_kids: int, break_name: Breakpoint
 ) -> Iterable[int]:
     if isinstance(x, int):
         y = [x]
@@ -266,9 +261,7 @@ def row_heights_attrs(
     # row height is derived from xs or defaults to auto in the CSS, so we don't need the
     # class to activate it
     classes = [
-        f"bslib-grid--row-heights--{brk}"
-        for brk in x_complete.keys()
-        if brk != Breakpoints.xs
+        f"bslib-grid--row-heights--{brk}" for brk in x_complete.keys() if brk != "xs"
     ]
 
     # Create CSS variables, treating numeric values as fractional units, passing strings