diff --git a/core/scripts/dev/commit-code-check.sh b/core/scripts/dev/commit-code-check.sh
index 7252c9364bd..4e1211b2657 100755
--- a/core/scripts/dev/commit-code-check.sh
+++ b/core/scripts/dev/commit-code-check.sh
@@ -123,8 +123,31 @@ fi;
 # run and all dependencies are updated.
 FINAL_STATUS=0
 
-# Check all files for spelling in one go for better performance.
+DEPENDENCIES_NEED_INSTALLING=0
+# Ensure PHP development dependencies are installed.
+# @todo https://github.com/composer/composer/issues/4497 Improve this to
+#  determine if dependencies in the lock file match the installed versions.
+#  Using composer install --dry-run is not valid because it would depend on
+#  user-facing strings in Composer.
+if ! [[ -f 'vendor/bin/phpcs' ]]; then
+  printf "Drupal's PHP development dependencies are not installed. Run 'composer install' from the root directory.\n"
+  DEPENDENCIES_NEED_INSTALLING=1;
+fi
+
 cd "$TOP_LEVEL/core"
+
+# Ensure JavaScript development dependencies are installed.
+yarn check -s 2>/dev/null
+if [ "$?" -ne "0" ]; then
+  printf "Drupal's JavaScript development dependencies are not installed. Run 'yarn install' inside the core directory.\n"
+  DEPENDENCIES_NEED_INSTALLING=1;
+fi
+
+if [ $DEPENDENCIES_NEED_INSTALLING -ne 0 ]; then
+  exit 1;
+fi
+
+# Check all files for spelling in one go for better performance.
 yarn run -s spellcheck -c $TOP_LEVEL/core/.cspell.json $ABS_FILES
 if [ "$?" -ne "0" ]; then
   # If there are failures set the status to a number other than 0.