diff --git a/ioc/modules/common.nix b/ioc/modules/common.nix
index a863e2a3..d98303da 100644
--- a/ioc/modules/common.nix
+++ b/ioc/modules/common.nix
@@ -27,7 +27,7 @@ with lib; {
           ~ The actual build of this distribution.
       '';
       default = {};
-      type = types.attrs;
+      type = with types; attrsOf package;
     };
 
     epnix.pkgs = mkOption {
diff --git a/ioc/modules/outputs.nix b/ioc/modules/outputs.nix
index 34865ca6..41f56887 100644
--- a/ioc/modules/outputs.nix
+++ b/ioc/modules/outputs.nix
@@ -3,6 +3,7 @@
   lib,
   pkgs,
   epnix,
+  epnixFunEval,
   ...
 }:
 with lib; let
@@ -19,25 +20,42 @@ with lib; let
     toUpper
   ];
 in {
-  options.epnix.buildConfig = {
-    attrs = mkOption {
-      description = "Extra attributes to pass to the derivation";
-      type = types.attrs;
-      default = {};
-    };
+  options.epnix = {
+    buildConfig = {
+      attrs = mkOption {
+        description = "Extra attributes to pass to the derivation";
+        type = types.attrs;
+        default = {};
+      };
+
+      src = mkOption {
+        description = ''
+          The source code for the top.
 
-    src = mkOption {
-      description = ''
-        The source code for the top.
+          Defaults to the directory containing the `flake.nix` file.
+        '';
+        type = types.path;
+      };
+    };
 
-        Defaults to the directory containing the `flake.nix` file.
-      '';
-      type = types.path;
+    generatedOverlay = mkOption {
+      description = "A generated overlay which has your package inside `pkgs.epnix.support`.";
+      type = with types; functionTo (functionTo attrs);
     };
   };
 
   config.epnix.buildConfig.src = mkDefault config.epnix.inputs.self;
 
+  config.epnix.generatedOverlay = final: prev: let
+    newEval = final.callPackage epnixFunEval final;
+  in {
+    epnix = prev.epnix.extend (_final: prev: {
+      support = prev.support.extend (_final: _prev: {
+        "${config.epnix.meta.name}" = newEval.config.epnix.outputs.build;
+      });
+    });
+  };
+
   config.epnix.outputs.build = pkgs.mkEpicsPackage ({
       pname = "epnix-${config.epnix.meta.name}";
       inherit (config.epnix.meta) version;
diff --git a/lib/default.nix b/lib/default.nix
index 1edfd521..38ed4520 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -7,71 +7,13 @@
 with lib; let
   self = {
     documentation = import ./documentation.nix args;
+    evaluation = import ./evaluation.nix args;
     formats = import ./formats.nix args;
     licenses = import ./licenses.nix args;
     maintainers = import ./maintainers/maintainer-list.nix;
     testing = import ./testing.nix;
 
-    evalEpnixModules = {
-      nixpkgsConfig,
-      epnixConfig,
-    }: let
-      nixpkgsConfigWithDefaults =
-        {
-          crossSystem = null;
-          config = {};
-        }
-        // nixpkgsConfig;
-      eval = evalModules {
-        modules = [
-          ({config, ...}: {
-            config._module.args = let
-              # Configure the available packages with e.g. cross compilation
-              # and overlays
-              finalPkgs = import inputs.nixpkgs {
-                inherit (nixpkgsConfigWithDefaults) system crossSystem config;
-                inherit (config.nixpkgs) overlays;
-              };
-            in {
-              # See: https://github.com/NixOS/nixpkgs/pull/190358
-              pkgs = finalPkgs.__splicedPackages;
-
-              # Used when we want to apply the same config in checks
-              inherit epnixConfig;
-            };
-          })
-
-          epnixConfig
-          inputs.self.nixosModules.ioc
-
-          # nixpkgs and assertions are separate, in case we want to include
-          # this module in a NixOS configuration, where `nixpkgs` and
-          # `assertions` options are already defined
-          ../ioc/modules/nixpkgs.nix
-          ../ioc/modules/assertions.nix
-        ];
-      };
-
-      # From Robotnix
-      # From nixpkgs/nixos/modules/system/activation/top-level.nix
-      failedAssertions = map (x: x.message) (lib.filter (x: !x.assertion) eval.config.assertions);
-
-      config =
-        if failedAssertions != []
-        then throw "\nFailed assertions:\n${lib.concatStringsSep "\n" (map (x: "- ${x}") failedAssertions)}"
-        else lib.showWarnings eval.config.warnings eval.config;
-    in {
-      inherit (eval) options;
-      inherit config;
-
-      inherit (config.epnix) outputs;
-    };
-
-    mkEpnixBuild = cfg:
-      (self.evalEpnixModules cfg).config.epnix.outputs.build;
-
-    mkEpnixDevShell = cfg:
-      (self.evalEpnixModules cfg).config.epnix.outputs.devShell;
+    inherit (self.evaluation) evalEpnixModules mkEpnixBuild mkEpnixDevShell;
 
     # Like lib.getName, but also supports paths
     getName = thing:
diff --git a/lib/evaluation.nix b/lib/evaluation.nix
new file mode 100644
index 00000000..8e9cc6dd
--- /dev/null
+++ b/lib/evaluation.nix
@@ -0,0 +1,95 @@
+{
+  inputs,
+  lib,
+  ...
+}: let
+  evalEpnixModules' = {
+    epnixConfig,
+    epnixFunEval,
+    pkgs,
+  }: let
+    eval = lib.evalModules {
+      modules = [
+        ({config, ...}: {
+          config._module.args = {
+            pkgs = pkgs config;
+
+            # Used when we want to apply the same config in checks
+            inherit epnixConfig;
+            inherit epnixFunEval;
+          };
+        })
+
+        epnixConfig
+        inputs.self.nixosModules.ioc
+
+        # nixpkgs and assertions are separate, in case we want to include
+        # this module in a NixOS configuration, where `nixpkgs` and
+        # `assertions` options are already defined
+        ../ioc/modules/nixpkgs.nix
+        ../ioc/modules/assertions.nix
+      ];
+    };
+
+    # From Robotnix
+    # From nixpkgs/nixos/modules/system/activation/top-level.nix
+    failedAssertions = map (x: x.message) (lib.filter (x: !x.assertion) eval.config.assertions);
+
+    config =
+      if failedAssertions != []
+      then throw "\nFailed assertions:\n${lib.concatStringsSep "\n" (map (x: "- ${x}") failedAssertions)}"
+      else lib.showWarnings eval.config.warnings eval.config;
+  in {
+    inherit (eval) options;
+    inherit config;
+
+    inherit (config.epnix) outputs generatedOverlay;
+  };
+
+  self = {
+    evalEpnixModules = {
+      nixpkgsConfig,
+      epnixConfig,
+    }: let
+      nixpkgsConfigWithDefaults =
+        {
+          crossSystem = null;
+          config = {};
+        }
+        // nixpkgsConfig;
+
+      pkgs = config:
+        (import inputs.nixpkgs {
+          inherit (nixpkgsConfigWithDefaults) system crossSystem config;
+          inherit (config.nixpkgs) overlays;
+        })
+        # See: https://github.com/NixOS/nixpkgs/pull/190358
+        .__splicedPackages;
+
+      # As a function,
+      # so that we can import the package without fixing the dependencies.
+      #
+      # This is needed because,
+      # if this package is an EPICS support module,
+      # it needs to *not* depend on a specific version of epics-base.
+      #
+      # It needs to use the same version of epics-base
+      # that is going to be used by the final IOC.
+      epnixFunEval = pkgs:
+        evalEpnixModules' {
+          inherit epnixConfig epnixFunEval;
+          pkgs = config: pkgs;
+        };
+
+      fixedEval = evalEpnixModules' {inherit epnixConfig epnixFunEval pkgs;};
+    in
+      fixedEval;
+
+    mkEpnixBuild = cfg:
+      (self.evalEpnixModules cfg).config.epnix.outputs.build;
+
+    mkEpnixDevShell = cfg:
+      (self.evalEpnixModules cfg).config.epnix.outputs.devShell;
+  };
+in
+  self
diff --git a/templates/top/flake.nix b/templates/top/flake.nix
index a1cb68d4..3be88393 100644
--- a/templates/top/flake.nix
+++ b/templates/top/flake.nix
@@ -4,6 +4,14 @@
   inputs.flake-utils.url = "github:numtide/flake-utils";
   inputs.epnix.url = "github:epics-extensions/epnix";
 
+  # If you have a support module as a separate EPNix repository,
+  # add it as an input here:
+  # ---
+  #inputs.mySupportModule = {
+  #  url = "git+ssh://git@my-server.org/me/exampleApp.git";
+  #  inputs.epnix.follows = "epnix";
+  #};
+
   # If you have an "App" as a separate repository,
   # add it as an input here:
   # ---
@@ -18,10 +26,15 @@
     epnix,
     ...
   } @ inputs: let
-    myEpnixDistribution = {pkgs, ...}: {
+    myEpnixConfig = {pkgs, ...}: {
       # Set your EPNix options here
       # ---
 
+      # If you have a support module as a separate EPNix repository,
+      # uncomment this line to make the package available:
+      # ---
+      #overlays = [inputs.mySupportModule.overlays.default];
+
       epnix = {
         inherit inputs;
 
@@ -33,9 +46,9 @@
         # ---
         #epics-base.releaseBranch = "3"; # Defaults to "7"
 
-        # Add one of the supported modules here:
+        # Add your support modules here:
         # ---
-        #support.modules = with pkgs.epnix.support; [ StreamDevice ];
+        #support.modules = with pkgs.epnix.support; [ StreamDevice mySupportModule ];
 
         # If you have an "App" as a separate repository,
         # add it here:
@@ -69,7 +82,7 @@
     # environment can be built on your machine.
     flake-utils.lib.eachSystem ["x86_64-linux"] (system:
       with epnix.lib; let
-        result = evalEpnixModules {
+        epnixDistribution = evalEpnixModules {
           nixpkgsConfig = {
             # This specifies the build architecture
             inherit system;
@@ -81,17 +94,23 @@
             # ---
             #crossSystem = epnix.inputs.nixpkgs.lib.systems.examples.armv7l-hf-multiplatform;
           };
-          epnixConfig = myEpnixDistribution;
+          epnixConfig = myEpnixConfig;
         };
       in {
         packages =
-          result.outputs
+          epnixDistribution.outputs
           // {
             default = self.packages.${system}.build;
           };
 
+        inherit epnixDistribution;
+
         devShells.default = self.packages.${system}.devShell;
 
-        checks = result.config.epnix.checks.derivations;
-      });
+        checks = epnixDistribution.config.epnix.checks.derivations;
+      })
+    // {
+      overlays.default = final: prev:
+        self.epnixDistribution.x86_64-linux.generatedOverlay final prev;
+    };
 }