diff --git a/modules/checks.nix b/modules/checks.nix
index f20bd56..39f653a 100644
--- a/modules/checks.nix
+++ b/modules/checks.nix
@@ -2,7 +2,6 @@
 let
   inherit (lib)
     filterAttrs
-    genAttrs
     mapAttrs
     mkOption
     optionalAttrs
@@ -30,7 +29,7 @@ in
         (k: v: v.checks)
         (filterAttrs
           (k: v: v.checks != null)
-          (genAttrs config.systems config.perSystem)
+          config.allSystems
         );
 
     perInput = system: flake:
diff --git a/modules/devShell.nix b/modules/devShell.nix
index 27534db..4f347c3 100644
--- a/modules/devShell.nix
+++ b/modules/devShell.nix
@@ -2,7 +2,6 @@
 let
   inherit (lib)
     filterAttrs
-    genAttrs
     mapAttrs
     mkOption
     optionalAttrs
@@ -25,13 +24,7 @@ in
     };
   };
   config = {
-    flake.devShell =
-      mapAttrs
-        (k: v: v.devShell)
-        (filterAttrs
-          (k: v: v.devShell != null)
-          (genAttrs config.systems config.perSystem)
-        );
+    flake.devShell = mapAttrs (k: v: v.devShell) config.allSystems;
 
     perInput = system: flake:
       optionalAttrs (flake?devShell.${system}) {
@@ -42,7 +35,8 @@ in
       _file = ./devShell.nix;
       options = {
         devShell = mkOption {
-          type = types.nullOr types.package;
+          type = types.package;
+          default = throw "The default devShell was not configured for system ${system}. Please set it, or if you don't want to use the devShell attribute, set flake.devShell = lib.mkForce {};";
           description = ''
             A derivation that nix develop bases its environment on.
           '';
diff --git a/modules/flake.nix b/modules/flake.nix
index 7202bee..2fe871c 100644
--- a/modules/flake.nix
+++ b/modules/flake.nix
@@ -2,7 +2,6 @@
 let
   inherit (lib)
     filterAttrs
-    genAttrs
     mapAttrs
     mkOption
     optionalAttrs
diff --git a/modules/legacyPackages.nix b/modules/legacyPackages.nix
index 492984d..1c66b31 100644
--- a/modules/legacyPackages.nix
+++ b/modules/legacyPackages.nix
@@ -2,7 +2,6 @@
 let
   inherit (lib)
     filterAttrs
-    genAttrs
     mapAttrs
     mkOption
     optionalAttrs
@@ -30,7 +29,7 @@ in
         (k: v: v.legacyPackages)
         (filterAttrs
           (k: v: v.legacyPackages != null)
-          (genAttrs config.systems config.perSystem)
+          config.allSystems
         );
 
     perInput = system: flake:
diff --git a/modules/packages.nix b/modules/packages.nix
index 3829800..d3352fb 100644
--- a/modules/packages.nix
+++ b/modules/packages.nix
@@ -2,7 +2,6 @@
 let
   inherit (lib)
     filterAttrs
-    genAttrs
     mapAttrs
     mkOption
     optionalAttrs
@@ -31,7 +30,7 @@ in
         (k: v: v.packages)
         (filterAttrs
           (k: v: v.packages != null)
-          (genAttrs config.systems config.perSystem)
+          config.allSystems
         );
 
     perInput = system: flake:
diff --git a/modules/perSystem.nix b/modules/perSystem.nix
index 5fcf86e..5632b9b 100644
--- a/modules/perSystem.nix
+++ b/modules/perSystem.nix
@@ -1,6 +1,7 @@
 { config, lib, self, ... }:
 let
   inherit (lib)
+    genAttrs
     mapAttrs
     mkOption
     types
@@ -36,7 +37,19 @@ in
         shorthandOnlyDefinesConfig = false;
       });
     };
+
+    allSystems = mkOption {
+      type = types.lazyAttrsOf types.unspecified;
+      description = "The system-specific config for each of systems.";
+      internal = true;
+    };
+  };
+
+  config = {
+    perSystem = system: { _module.args.system = system; };
+    allSystems = genAttrs config.systems config.perSystem;
+    # TODO: Sub-optimal error message. Get Nix to support a memoization primop, or get Nix Flakes to support systems properly or get Nix Flakes to add a name to flakes.
+    _module.args.getSystem = system: config.allSystems.${system} or builtins.trace "using non-memoized system ${system}" config.perSystem system;
   };
 
-  config.perSystem = system: { _module.args.system = system; };
 }