diff --git a/run-build-functions.sh b/run-build-functions.sh
index 5d84faf6..db7a49c1 100755
--- a/run-build-functions.sh
+++ b/run-build-functions.sh
@@ -76,6 +76,7 @@ mkdir -p $NETLIFY_CACHE_DIR/.cargo
 : ${NPM_FLAGS=""}
 : ${PNPM_FLAGS=""}
 : ${BUNDLER_FLAGS=""}
+: ${COMPOSER_FLAGS=""}
 
 # Feature flags are a comma-separated list.
 # The following logic relies on the fact that feature flags cannot currently
@@ -291,6 +292,10 @@ run_npm() {
   export PATH=$(npm bin):$PATH
 }
 
+run_composer() {
+  composer install ${COMPOSER_FLAGS:+$COMPOSER_FLAGS}
+}
+
 install_node() {
   local defaultNodeVersion=$1
   local featureFlags=$2
@@ -773,7 +778,7 @@ install_dependencies() {
   if [ -f composer.json ]
   then
     restore_home_cache ".composer" "composer dependencies"
-    composer install
+    run_composer
   fi
 
   install_go $installGoVersion
diff --git a/tests/php/composer.bats b/tests/php/composer.bats
new file mode 100644
index 00000000..e73925cf
--- /dev/null
+++ b/tests/php/composer.bats
@@ -0,0 +1,35 @@
+#!/usr/bin/env bats
+
+load "../helpers.sh"
+
+load '../../node_modules/bats-support/load'
+load '../../node_modules/bats-assert/load'
+load '../../node_modules/bats-file/load'
+
+setup() {
+  TMP_DIR=$(setup_tmp_dir)
+  set_fixture_as_repo 'simple-php' "$TMP_DIR"
+
+  # Load functions
+  load '../../run-build-functions.sh'
+}
+
+teardown() {
+  rm -rf "$TMP_DIR"
+  # Return to original dir
+  cd - || return
+}
+
+@test 'composer install' {
+  run run_composer
+  assert_success
+  assert_output --partial "(including require-dev)"
+}
+
+@test 'composer install with flags' {
+  COMPOSER_FLAGS="--no-dev"
+
+  run run_composer
+  assert_success
+  refute_output --partial "(including require-dev)"
+}
\ No newline at end of file
diff --git a/tests/php/fixtures/simple-php/composer.json b/tests/php/fixtures/simple-php/composer.json
new file mode 100644
index 00000000..e5c748f9
--- /dev/null
+++ b/tests/php/fixtures/simple-php/composer.json
@@ -0,0 +1,4 @@
+{
+    "name": "fixture/simple-php",
+    "require": {}
+}