diff --git a/specs.md b/specs.md
index 3092839..4b1d5f1 100644
--- a/specs.md
+++ b/specs.md
@@ -1206,7 +1206,7 @@ write_fd :: (fd: i32, buf: [*]u8, count: u64) -> i64 #foreign libc "write";
 ```
 
 - `#library "name"` must be assigned to a named constant. The library is passed to the linker (`-lname` on Unix, `name.lib` on Windows).
-- `#foreign lib_ref` declares a function as external C. The library reference is mandatory.
+- `#foreign lib_ref` declares a function as external C. The library reference is optional: when present it is passed to the linker (`-lname` on Unix); when omitted (`name :: (…) -> T #foreign;`), the symbol must resolve at link time from a framework or an already-linked / auto-detected library.
 - `#foreign lib_ref "c_symbol"` renames the binding: the sx function name differs from the C symbol. This avoids name collisions (e.g. POSIX `write` vs an sx builtin).
 
 ### C Interop Type Mapping