diff --git a/modules/caddyhttp/reverseproxy/healthchecks.go b/modules/caddyhttp/reverseproxy/healthchecks.go
index 888dadb7..ac92604c 100644
--- a/modules/caddyhttp/reverseproxy/healthchecks.go
+++ b/modules/caddyhttp/reverseproxy/healthchecks.go
@@ -386,6 +386,7 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, upstre
 
 	// set headers, using a replacer with only globals (env vars, system info, etc.)
 	repl := caddy.NewReplacer()
+	repl.Set("http.reverse_proxy.active.target_host", hostAddr)
 	for key, vals := range h.HealthChecks.Active.Headers {
 		key = repl.ReplaceAll(key, "")
 		if key == "Host" {