diff --git a/nix/devshell.nix b/nix/devshell.nix
index 0d3400aa..d7562084 100644
--- a/nix/devshell.nix
+++ b/nix/devshell.nix
@@ -20,6 +20,11 @@
         rust-analyzer
         rustc
         rustfmt
+        # The two "prose lint (vale)" CI jobs run vale over docs/. `vale
+        # sync` must run once before `vale docs` and writes styles to
+        # $XDG_DATA_HOME, so point that at the repo like CI does:
+        # `XDG_DATA_HOME=$PWD/.vale-data nix develop -c sh -c 'vale sync && vale docs'`.
+        vale
       ]);
 
     # `cargo llvm-cov` shells out to `llvm-profdata` and `llvm-cov`,