diff --git a/walk.go b/walk.go
index 06d5506..f2ddcfe 100644
--- a/walk.go
+++ b/walk.go
@@ -462,6 +462,11 @@ func (s *PromQLSmith) walkLabelMatchers() []*labels.Matcher {
 	})
 
 	valF := func(v string) string {
+		// If a label value contains + such as +Inf it will cause parse error for regex.
+		// Always hardcode to .+ for simplicity.
+		if strings.Contains(v, "+") {
+			return ".+"
+		}
 		val := s.rnd.Float64()
 		switch {
 		case val > 0.95: