diff --git a/core/modules/simpletest/simpletest.install b/core/modules/simpletest/simpletest.install
index 530228834a973e1821de7b2d3f3b6eb2c52603c1..4e0ea9b76db91e5193e515f0bb2df0b9f3327931 100644
--- a/core/modules/simpletest/simpletest.install
+++ b/core/modules/simpletest/simpletest.install
@@ -29,7 +29,7 @@ function simpletest_requirements($phase) {
   ];
   if (!$has_phpunit) {
     $requirements['phpunit']['severity'] = REQUIREMENT_ERROR;
-    $requirements['phpunit']['description'] = t("The testing framework requires the PHPUnit package. Please run 'composer install --dev' to ensure it is present.");
+    $requirements['phpunit']['description'] = t("The testing framework requires the PHPUnit package. Please run 'composer install' to ensure it is present.");
   }
 
   $requirements['curl'] = [
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index eb77e135f325b64b184bc5e9595966a3b88dd6fb..4916f8c4b721bf9bba56e5da93c2d5040bf04e32 100644
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -48,7 +48,7 @@
 simpletest_script_init();
 
 if (!class_exists(TestCase::class)) {
-  echo "\nrun-tests.sh requires the PHPUnit testing framework. Please use 'composer install --dev' to ensure that it is present.\n\n";
+  echo "\nrun-tests.sh requires the PHPUnit testing framework. Please use 'composer install' to ensure that it is present.\n\n";
   exit(SIMPLETEST_SCRIPT_EXIT_FAILURE);
 }