diff --git a/builder/make-config-files.nix b/builder/make-config-files.nix
index 02722535..dfeda719 100644
--- a/builder/make-config-files.nix
+++ b/builder/make-config-files.nix
@@ -6,10 +6,29 @@ let
     echo "${field}: ${lib.concatStringsSep " " xs}" >> $out/cabal.config
   '';
 
+  # This is a bit of a hack.  So we'll have a slightly longer explaination here:
+  # exactDep will pass --exact-configuration to the `SETUP_HS confiugre` command.
+  # This requires us to pass --dependency={dep name}={pkg id}.  The dependency
+  # name will usually be the name of the package `p`, which we can locate in the
+  # package-db, passed in via `pdbArg`.  Thus querying the package-db for the
+  # id field for package `p`, will unsually provide is with the right value.  Sublibs
+  # need a bit of special handling:
+  #
+  # - Sublibs: if the dependency is a sublibrary of a package, we need to use
+  #            the sublibrary's name for the dep name, and lookup the sublibraries
+  #            pkg id for z-{pkg name}-z-{sublib name}.  As we do not provide the
+  #            sublib name to exactDep, as we don't have access to it at the call-site,
+  #            we resort to a bit of globbing, which (as pkg db's should contain only
+  #            a single package) work.
   exactDep = pdbArg: p: ''
     if id=$(target-pkg ${pdbArg} field ${p} id --simple-output); then
       echo "--dependency=${p}=$id" >> $out/configure-flags
-    fi
+    elif id=$(target-pkg ${pdbArg} field "z-${p}-z-*" id --simple-output); then
+      name=$(target-pkg ${pdbArg} field "z-${p}-z-*" name --simple-output)
+      # so we are dealing with a sublib. As we build sublibs separately, the above
+      # query should be safe.
+      echo "--dependency=''${name#z-${p}-z-}=$id" >> $out/configure-flags
+    fi     
     if ver=$(target-pkg ${pdbArg} field ${p} version --simple-output); then
       echo "constraint: ${p} == $ver" >> $out/cabal.config
       echo "constraint: ${p} installed" >> $out/cabal.config
@@ -68,7 +87,7 @@ in { identifier, component, fullName, flags ? {} }:
     echo "allow-newer: ${identifier.name}:*" >> $out/cabal.config
     echo "allow-older: ${identifier.name}:*" >> $out/cabal.config
 
-    ${lib.concatMapStringsSep "\n" (p: exactDep "--package-db ${p.components.library}/package.conf.d" p.identifier.name) component.depends}
+    ${lib.concatMapStringsSep "\n" (p: exactDep "--package-db ${p.components.library or p}/package.conf.d" p.identifier.name) component.depends}
     ${lib.concatMapStringsSep "\n" (exactDep "") nonReinstallablePkgs}
 
   ''
diff --git a/default.nix b/default.nix
index 03abe1bf..0b744172 100644
--- a/default.nix
+++ b/default.nix
@@ -104,7 +104,9 @@ let
       in self.mkPkgSet {
         inherit pkg-def;
         pkg-def-extras = [ stack-pkgs.extras ] ++ pkg-def-extras;
-        modules = [ patchesModule ] ++ modules;
+        # set doExactConfig = true. The stackage set should be consistent
+        # and we should trust stackage here!
+        modules = [ { doExactConfig = true; } patchesModule ] ++ modules;
       };
 
     # Create a Haskell package set based on a Cabal configuration.
@@ -122,7 +124,9 @@ let
       in self.mkPkgSet {
         inherit pkg-def;
         pkg-def-extras = [ plan-pkgs.extras ] ++ pkg-def-extras;
-        modules = [ patchesModule ] ++ modules;
+        # set doExactConfig = true, as we trust cabals resolution for
+        # the plan.
+        modules = [ { doExactConfig = true; } patchesModule ] ++ modules;
       };
 
     # Package sets for all stackage snapshots.
diff --git a/modules/component-driver.nix b/modules/component-driver.nix
index 80cdc94b..54f877ac 100644
--- a/modules/component-driver.nix
+++ b/modules/component-driver.nix
@@ -13,8 +13,13 @@ in
   options.nonReinstallablePkgs = lib.mkOption {
     type = lib.types.listOf lib.types.str;
   };
+  options.reinstallableLibGhc = lib.mkOption {
+    type = lib.types.bool;
+    default = false;
+    description = "Is lib:ghc reinstallable?";
+  };
 
-  # Dependencies
+  # Dependencies (with reinstallable-lib:ghc)
   # 
   #              .--------.           .------------------.
   #              | pretty | < ------- | template-haskell |
@@ -31,10 +36,13 @@ in
   #       |       .-----.        |  '-- > |-------or-------|
   #       '---- > | rts | < -----'        | integer-gmp    |
   #               '-----'                 '----------------'
+  #
+  # without reinstallable-lib:ghc, this is significantly larger.
 
   config.nonReinstallablePkgs =
     [ "rts" "ghc-heap" "ghc-prim" "integer-gmp" "integer-simple" "base"
-      "deepseq" "array" "ghc-boot-th" "pretty" "template-haskell" ];
+      "deepseq" "array" "ghc-boot-th" "pretty" "template-haskell" ]
+    ++ lib.optional (!config.reinstallableLibGhc) "ghc";
 
   options.hsPkgs = lib.mkOption {
     type = lib.types.unspecified;