diff --git a/retrieval/targetmanager.go b/retrieval/targetmanager.go
index bf8b8cb22..0478875cb 100644
--- a/retrieval/targetmanager.go
+++ b/retrieval/targetmanager.go
@@ -404,6 +404,7 @@ func providersFromConfig(cfg *config.ScrapeConfig) map[string]TargetProvider {
 }
 
 // targetsFromGroup builds targets based on the given TargetGroup and config.
+// Panics if target group is nil.
 func targetsFromGroup(tg *config.TargetGroup, cfg *config.ScrapeConfig) ([]*Target, error) {
 	targets := make([]*Target, 0, len(tg.Targets))