diff --git a/src/pkg/testing/regexp.go b/src/pkg/testing/regexp.go
index de30a13f91..cd37699ce3 100644
--- a/src/pkg/testing/regexp.go
+++ b/src/pkg/testing/regexp.go
@@ -615,7 +615,7 @@ func CompileRegexp(str string) (regexp *Regexp, error string) {
 	regexp.expr = str
 	regexp.inst = make([]instr, 0, 20)
 	error = regexp.doParse()
-	if error != nil {
+	if error != "" {
 		regexp = nil
 	}
 	return