diff --git a/tests/scripts/key-exchanges.pl b/tests/scripts/key-exchanges.pl
index bfde0693a..9cfa2d398 100755
--- a/tests/scripts/key-exchanges.pl
+++ b/tests/scripts/key-exchanges.pl
@@ -45,7 +45,7 @@ for my $kex (@kexes) {
     print "\n******************************************\n";
     print "* Testing with key exchange: $kex\n";
     print "******************************************\n";
-    $ENV{MBEDTLS_TEST_CONFIGURATION} = "-$kex";
+    $ENV{MBEDTLS_TEST_CONFIGURATION} = $kex;
 
     # full config with all key exchanges disabled except one
     system( "scripts/config.pl full" ) and abort "Failed config full\n";
diff --git a/tests/scripts/test-ref-configs.pl b/tests/scripts/test-ref-configs.pl
index 5e110113b..1df84f74f 100755
--- a/tests/scripts/test-ref-configs.pl
+++ b/tests/scripts/test-ref-configs.pl
@@ -65,7 +65,7 @@ while( my ($conf, $data) = each %configs ) {
     print "\n******************************************\n";
     print "* Testing configuration: $conf\n";
     print "******************************************\n";
-    $ENV{MBEDTLS_TEST_CONFIGURATION} = "$conf";
+    $ENV{MBEDTLS_TEST_CONFIGURATION} = $conf;
 
     system( "cp configs/$conf $config_h" )
         and abort "Failed to activate $conf\n";