diff --git a/.travis.yml b/.travis.yml
index 6c4f9eb035..bf8d94f356 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,29 +1,28 @@
-# This file lints the code, builds a package and then deploys it.
-# For the deployment, $BINTRAY_USER, $BINTRAY_KEY and $GH_TOKEN environment
-# variables need to be set.
-language: php
+# This file lints the code, runs tests, builds a package and then deploys it.
+# The following environment variables need to be set:
+# - “$BINTRAY_USER” and “$BINTRAY_KEY” for pushing built package to Bintray
+# - “$GH_TOKEN” to avoid Composer being throttled by GitHub
+# - “$CACHIX_AUTH_TOKEN” for uploading built Nix packages to Cachix
+language: nix
+dist: focal
+nix: 2.3.9
+sudo: false
 
-dist: xenial
+env:
+    global:
+        - CACHIX_CACHE=fossar
+        - COMPOSER_NO_INTERACTION=1
 
 matrix:
     include:
-        - php: 8.0
-        - php: 7.4
-        - php: 7.3
-        - php: 7.2
-        - php: 7.1
-        - php: 7.0
-          env: CS_FIXER=true LINT_JS=true
-        - php: 5.6
-          env: DEPLOY=true
+        - env: PHP=80
+        - env: PHP=74
+        - env: PHP=73
+        - env: PHP=72
+        - env: PHP=71
+        - env: PHP=70 CS_FIXER=true LINT_JS=true
+        - env: PHP=56 DEPLOY=true
     fast_finish: true
-env:
-    - COMPOSER_NO_INTERACTION=1
-
-addons:
-    apt:
-        packages:
-            - jq
 
 cache:
     directories:
@@ -31,29 +30,37 @@ cache:
         - $HOME/.composer/cache
 
 before_install:
-    - nvm install 12
-    - pyenv install 3.6.3
-    - pyenv global 3.6.3
-    - pip3 install requests bcrypt
-    - if [ -n "$GH_TOKEN" ]; then composer config github-oauth.github.com ${GH_TOKEN}; fi
-    - composer self-update
+    # Nix & Cachix set-up.
+    - echo "trusted-users = $USER" | sudo tee -a /etc/nix/nix.conf
+    - sudo systemctl restart nix-daemon
+    - nix-env -iA nixpkgs.cachix
+    - cachix use $CACHIX_CACHE
+    - nix path-info --all > /tmp/store-path-pre-build
+
+    # Update flake.nix to match the current CI job from matrix.
+    - sed -i "s/matrix.php = \"php\";/matrix.php = \"php${PHP}\";/" flake.nix
+
+    - if [ -n "$GH_TOKEN" ]; then nix-shell --run "composer config github-oauth.github.com ${GH_TOKEN}"; fi
 
 install:
-    - phpenv config-rm xdebug.ini
-    - npm run install-dependencies
+    - nix-shell --run "npm run install-dependencies"
 
 script:
-    - if [ "$LINT_JS" = true ]; then npm run lint:client; fi
-    - npm run lint:server
-    - if [ "$CS_FIXER" = true ]; then npm run cs:server; fi
-    - npm run test:server
-    - npm run test:integration
+    - if [ "$LINT_JS" = true ]; then nix-shell --run "npm run lint:client"; fi
+    - nix-shell --run "npm run lint:server"
+    - if [ "$CS_FIXER" = true ]; then nix-shell --run "npm run cs:server"; fi
+    - nix-shell --run "npm run test:server"
+    - nix-shell --run "npm run test:integration"
+
+after_success:
+    # Upload built Nix packages to Cachix.
+    - comm -13 <(sort /tmp/store-path-pre-build | grep -v '\.drv$') <(nix path-info --all | grep -v '\.drv$' | sort) | cachix push $CACHIX_CACHE
 
 before_deploy:
     - git config --global user.email 'Travis CI'
     - git config --global user.name 'builds@travis-ci.org'
-    - source utils/package.sh
-    - source utils/bintray.sh
+    - nix-shell --run "source utils/package.sh"
+    - nix-shell --run "source utils/bintray.sh"
 
 deploy:
     - provider: bintray
diff --git a/flake.nix b/flake.nix
index d3f9364b49..9845ab0aad 100644
--- a/flake.nix
+++ b/flake.nix
@@ -14,6 +14,8 @@
 
   outputs = { self, flake-compat, nixpkgs, utils }:
     let
+      matrix.php = "php";
+
       mkDevShell = pkgs: phpPackage:
         let
           php = pkgs.${phpPackage}.withExtensions ({ enabled, all }: with all; enabled ++ [
@@ -31,6 +33,7 @@
               pkgs.zola
               pkgs.nodejs_latest
               python
+              pkgs.jq
             ] ++ (with php.packages; [
               composer
               psalm
@@ -50,7 +53,7 @@
           packages = {
             inherit (pkgs) php56 php70 php71 php72;
           };
-          devShell = mkDevShell pkgs "php";
+          devShell = mkDevShell pkgs matrix.php;
         }
       );
 }