diff --git a/scripts/run-tests.sh b/scripts/run-tests.sh
index cc09c76..f651f22 100755
--- a/scripts/run-tests.sh
+++ b/scripts/run-tests.sh
@@ -253,14 +253,14 @@ function simpletest_script_init($server_software) {
   if (!empty($args['php'])) {
     $php = $args['php'];
   }
-  elseif (!empty($_ENV['_'])) {
+  elseif ($php_env = getenv('_')) {
     // '_' is an environment variable set by the shell. It contains the command that was executed.
-    $php = $_ENV['_'];
+    $php = $php_env;
   }
-  elseif (!empty($_ENV['SUDO_COMMAND'])) {
+  elseif ($sudo = getenv('SUDO_COMMAND')) {
     // 'SUDO_COMMAND' is an environment variable set by the sudo program.
     // Extract only the PHP interpreter, not the rest of the command.
-    list($php, ) = explode(' ', $_ENV['SUDO_COMMAND'], 2);
+    list($php, ) = explode(' ', $sudo, 2);
   }
   else {
     simpletest_script_print_error('Unable to automatically determine the path to the PHP interpreter. Supply the --php command line argument.');