diff --git a/readme.md b/readme.md
index 712142d..80ea1da 100644
--- a/readme.md
+++ b/readme.md
@@ -114,7 +114,11 @@ function declaration, an `impl` method definition, or a `::` type declaration
 positions are exempt**: a struct *field*, a union *tag*, and a protocol
 *method-signature* may be a bare reserved spelling (`struct { s2: s64 }`,
 `union { u8: … }`, `protocol { s2 :: (self) }`) — they are reached via `obj.name`,
-so they never mis-lower. A leading backtick escapes one into a **raw identifier**:
+so they never mis-lower. The bare exemption covers only the identifier-classified
+reserved names (`s1`..`s64`, `u1`..`u64`, `bool`, `string`, `void`, `usize`,
+`isize`, `Any`); `f32` and `f64` are lexer keywords, so even in a member slot they
+need the backtick (`` struct { `f32: s64 } ``). A leading backtick escapes one into
+a **raw identifier**:
 `` `name `` is the literal identifier `name` (the backtick drops out of the text),
 usable in **every** position — value, declaration, and type, and optional in the
 exempt member positions. It is the only way handwritten sx can spell a reserved
diff --git a/specs.md b/specs.md
index 583943e..3683a57 100644
--- a/specs.md
+++ b/specs.md
@@ -38,6 +38,15 @@ and `` obj.`s2 `` both resolve. The exemption covers member *signatures* only: a
 slot), so a reserved-spelled impl method still needs the backtick
 (`` `s2 :: (self) ``), exactly like a free function. See `examples/0158`.
 
+The bare member-name exemption applies only to the **identifier-classified**
+reserved spellings — `s1`..`s64`, `u1`..`u64`, `bool`, `string`, `void`, `usize`,
+`isize`, `Any` — which all lex as ordinary identifiers. The two
+**keyword-classified** reserved spellings, `f32` and `f64`, are lexer keywords, and
+member-name slots require an identifier token; a bare `f32` / `f64` is therefore
+rejected at parse (`expected field name in struct`) even in a member position. Use
+the backtick there too — `` struct { `f32: s64; } `` / `` union { `f64: … } `` /
+`` protocol { `f32 :: (self); } `` work as field / tag / method names.
+
 ```sx
 s2 := 2.5;                          // ERROR: 's2' is a reserved type name and cannot be used as an identifier
 s2 :: 5;                            // ERROR — a `::` constant name is a binding site too