diff --git a/src/expvar/expvar.go b/src/expvar/expvar.go
index 954d63d17f52b1..5e9034e5d7a976 100644
--- a/src/expvar/expvar.go
+++ b/src/expvar/expvar.go
@@ -4,7 +4,8 @@
 
 // Package expvar provides a standardized interface to public variables, such
 // as operation counters in servers. It exposes these variables via HTTP at
-// /debug/vars in JSON format.
+// /debug/vars in JSON format. As of Go 1.22, the /debug/vars request must
+// use GET.
 //
 // Operations to set or modify these public variables are atomic.
 //
@@ -23,6 +24,7 @@ package expvar
 
 import (
 	"encoding/json"
+	"internal/godebug"
 	"log"
 	"math"
 	"net/http"
@@ -381,7 +383,11 @@ func memstats() any {
 }
 
 func init() {
-	http.HandleFunc("/debug/vars", expvarHandler)
+	if godebug.New("httpmuxgo121").Value() == "1" {
+		http.HandleFunc("/debug/vars", expvarHandler)
+	} else {
+		http.HandleFunc("GET /debug/vars", expvarHandler)
+	}
 	Publish("cmdline", Func(cmdline))
 	Publish("memstats", Func(memstats))
 }