diff --git a/system/etc.nix b/system/etc.nix
index fd64411163b..4dec5ff61ea 100644
--- a/system/etc.nix
+++ b/system/etc.nix
@@ -79,29 +79,28 @@ import ../helpers/make-etc.nix {
 
     { # Configuration file for fontconfig used to locate
       # (X11) client-rendered fonts.
-      source = pkgs.substituteAll {
-        src = ./etc/fonts/fonts.conf;
-        fontDirectories =
-          let
-            # Search for fonts in...
-            runtimeDirs = [
-              # - the user's .fonts directory
-              "~/.fonts"
-              # - the user's current profile
-              "~/.nix-profile/lib/X11/fonts"
-              # - the default profile
-              "/nix/var/nix/profiles/default/lib/X11/fonts"
-            ];
-            systemFonts = [
-              # - a few statically built locations
-              pkgs.xorg.fontbhttf
-              pkgs.xorg.fontbh100dpi
-              pkgs.xorg.fontbhlucidatypewriter100dpi
-              pkgs.freefont_ttf
-            ];
-          in
-            map (dir: "<dir>${dir}</dir>") (runtimeDirs ++ systemFonts);
-      };
+      source = pkgs.runCommand "fonts.conf"
+        { 
+          fontDirectories = [
+            # - the user's .fonts directory
+            "~/.fonts"
+            # - the user's current profile
+            "~/.nix-profile/lib/X11/fonts"
+            # - the default profile
+            "/nix/var/nix/profiles/default/lib/X11/fonts"
+            # - a few statically built locations
+            pkgs.xorg.fontbhttf
+            pkgs.xorg.fontbh100dpi
+            pkgs.xorg.fontbhlucidatypewriter100dpi
+            pkgs.freefont_ttf
+          ];
+          buildInputs = [pkgs.libxslt];
+          inherit (pkgs) fontconfig;
+        }
+        "xsltproc --stringparam fontDirectories \"$fontDirectories\" \\
+            ${./etc/fonts/make-fonts-conf.xsl} $fontconfig/etc/fonts/fonts.conf \\
+            > $out
+        ";
       target = "fonts/fonts.conf";
     }
 
diff --git a/system/etc/fonts/fonts.conf b/system/etc/fonts/fonts.conf
deleted file mode 100644
index 70d886e08cd..00000000000
--- a/system/etc/fonts/fonts.conf
+++ /dev/null
@@ -1,8 +0,0 @@
-<?xml version="1.0"?>
-<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
-
-<fontconfig>
-
-  @fontDirectories@
-
-</fontconfig>
diff --git a/system/etc/fonts/make-fonts-conf.xsl b/system/etc/fonts/make-fonts-conf.xsl
new file mode 100644
index 00000000000..22ecbc67039
--- /dev/null
+++ b/system/etc/fonts/make-fonts-conf.xsl
@@ -0,0 +1,32 @@
+<?xml version="1.0"?>
+
+<!--
+  This script copies the original fonts.conf from the fontconfig
+  distribution, but replaces all <dir> entries with the directories
+  specified in the $fontDirectories parameter.
+-->
+
+<xsl:stylesheet version="1.0"
+                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+                xmlns:str="http://exslt.org/strings"
+                extension-element-prefixes="str"
+                >
+
+  <xsl:output method='xml' encoding="UTF-8" doctype-system="fonts.dtd" />
+
+  <xsl:param name="fontDirectories" />
+
+  <xsl:template match="/fontconfig">
+
+    <fontconfig>
+      <xsl:copy-of select="child::node()[name() != 'dir']" />
+
+      <xsl:for-each select="str:tokenize($fontDirectories)">
+        <dir><xsl:value-of select="." /></dir>
+      </xsl:for-each>
+      
+    </fontconfig>
+
+  </xsl:template>
+  
+</xsl:stylesheet>
\ No newline at end of file