diff --git a/flake.nix b/flake.nix
index 2a90e61..0e8ca23 100644
--- a/flake.nix
+++ b/flake.nix
@@ -87,6 +87,25 @@
 
       formatter = eachSystemMap systems (system: treefmtEval.${system}.config.build.wrapper);
 
+      # Regression check: force snowfall-lib evaluation so unexpected-arg errors fail in `nix flake check`.
+      checks = eachSystemMap systems (
+        system:
+        let
+          pkgs = inputs.nixpkgs.legacyPackages.${system};
+          lib = mkLib {
+            src = self;
+            inputs = inputs // {
+              self = { };
+            };
+          };
+          eval = builtins.tryEval (builtins.attrNames lib.snowfall);
+        in
+        assert eval.success;
+        {
+          snowfall-lib-eval = pkgs.runCommand "snowfall-lib-eval" { } "mkdir -p $out";
+        }
+      );
+
       snowfall = rec {
         raw-config = config;
 
diff --git a/snowfall-lib/attrs/default.nix b/snowfall-lib/attrs/default.nix
index 52758d7..61ae25a 100644
--- a/snowfall-lib/attrs/default.nix
+++ b/snowfall-lib/attrs/default.nix
@@ -1,5 +1,6 @@
 {
   core-inputs,
+  ...
 }:
 let
   inherit (core-inputs.nixpkgs.lib)
diff --git a/snowfall-lib/checks/default.nix b/snowfall-lib/checks/default.nix
index bd5a8e4..b94e454 100644
--- a/snowfall-lib/checks/default.nix
+++ b/snowfall-lib/checks/default.nix
@@ -1,5 +1,6 @@
 {
   snowfall-lib,
+  ...
 }:
 {
   check = {
diff --git a/snowfall-lib/fp/default.nix b/snowfall-lib/fp/default.nix
index 9f6e9b6..65130e7 100644
--- a/snowfall-lib/fp/default.nix
+++ b/snowfall-lib/fp/default.nix
@@ -1,5 +1,6 @@
 {
   core-inputs,
+  ...
 }:
 let
   inherit (core-inputs.nixpkgs.lib) id foldr flip;
diff --git a/snowfall-lib/path/default.nix b/snowfall-lib/path/default.nix
index 7d7f7b0..09c2b45 100644
--- a/snowfall-lib/path/default.nix
+++ b/snowfall-lib/path/default.nix
@@ -1,6 +1,7 @@
 {
   core-inputs,
   snowfall-lib,
+  ...
 }:
 let
   inherit (builtins)
diff --git a/snowfall-lib/shell/default.nix b/snowfall-lib/shell/default.nix
index f160d10..087552e 100644
--- a/snowfall-lib/shell/default.nix
+++ b/snowfall-lib/shell/default.nix
@@ -1,5 +1,6 @@
 {
   snowfall-lib,
+  ...
 }:
 {
   shell = {
diff --git a/snowfall-lib/template/default.nix b/snowfall-lib/template/default.nix
index 70d717d..8e09e3d 100644
--- a/snowfall-lib/template/default.nix
+++ b/snowfall-lib/template/default.nix
@@ -1,6 +1,6 @@
 {
-  core-inputs,
   snowfall-lib,
+  ...
 }:
 let