diff --git a/flake.nix b/flake.nix
index 230a14c..d9c9b57 100644
--- a/flake.nix
+++ b/flake.nix
@@ -35,17 +35,31 @@
 
           buildInputs = commonBuildInputs;
 
+          phases = [
+            "unpackPhase"
+            "installPhase"
+            "buildPhase"
+          ];
+
+          installPhase = ''
+            runHook preInstall
+
+            rst2pdf slides.rst \
+              --break-level 1 \
+              --extension-module preprocess \
+              --fit-background-mode scale \
+              --font-path "${toString shared}/fonts" \
+              --output slides.pdf \
+              --stylesheets bw,"${toString shared}/styles/opdavies-light"
+
+            runHook postInstall
+          '';
+
           buildPhase = ''
             runHook preBuild
 
             mkdir $out
-
-            rst2pdf slides.rst \
-              --break-level 1 \
-              --fit-background-mode scale \
-              --font-path "${toString shared}/fonts" \
-              --output "$out/slides.pdf" \
-              --stylesheets bw,"${toString shared}/styles/opdavies-light"
+            cp slides.pdf $out
 
             runHook postBuild
           '';