diff --git a/tests/runner.pm b/tests/runner.pm
index 8ebb855ca6..115d078a1f 100644
--- a/tests/runner.pm
+++ b/tests/runner.pm
@@ -709,6 +709,9 @@ sub singletest_precheck {
                 $cmd = join(" ", @p);
             }
 
+            # provide an environment variable
+            $ENV{'CURL_TESTNUM'} = $testnum;
+
             my @o = `$cmd 2> $LOGDIR/precheck-$testnum`;
             if($o[0]) {
                 $why = $o[0];