diff --git a/.sqlfluff b/.sqlfluff
deleted file mode 100644
index 391f553..0000000
--- a/.sqlfluff
+++ /dev/null
@@ -1,6 +0,0 @@
-[sqlfluff]
-dialect = postgres
-# LT05 (line too long) is unfixable for long function signatures and seed
-# rows, which makes `sqlfluff format` exit non-zero. Exclude it so it acts
-# purely as a formatter under treefmt.
-exclude_rules = LT05
diff --git a/devenv.nix b/devenv.nix
index ed18882..ead0fce 100644
--- a/devenv.nix
+++ b/devenv.nix
@@ -24,10 +24,8 @@
     "app:check".exec = "bin/rake"; # default: test + mutate_since
   };
 
-  # treefmt drives all formatters (Ruby via syntax_tree, SQL via sqlfluff).
   treefmt.enable = true;
   treefmt.config = {
-    projectRootFile = "devenv.nix";
     settings.formatter = {
       ruby = {
         command = "stree";
@@ -36,7 +34,13 @@
       };
       sql = {
         command = "sqlfluff";
-        options = [ "format" ];
+        options = [
+          "format"
+          "--dialect"
+          "postgres"
+          "--exclude-rules"
+          "LT05"
+        ];
         includes = [ "db/**/*.sql" ];
       };
     };