diff --git a/modules/caddyhttp/reverseproxy/httptransport.go b/modules/caddyhttp/reverseproxy/httptransport.go
index 24407df2b..6729ea2fb 100644
--- a/modules/caddyhttp/reverseproxy/httptransport.go
+++ b/modules/caddyhttp/reverseproxy/httptransport.go
@@ -171,12 +171,25 @@ func (HTTPTransport) CaddyModule() caddy.ModuleInfo {
 	}
 }
 
+var (
+	allowedVersions       = []string{"1.1", "2", "h2c", "3"}
+	allowedVersionsString = strings.Join(allowedVersions, ", ")
+)
+
 // Provision sets up h.Transport with a *http.Transport
 // that is ready to use.
 func (h *HTTPTransport) Provision(ctx caddy.Context) error {
 	if len(h.Versions) == 0 {
 		h.Versions = []string{"1.1", "2"}
 	}
+	// some users may provide http versions not recognized by caddy, instead of trying to
+	// guess the version, we just error out and let the user fix their config
+	// see: https://github.com/caddyserver/caddy/issues/7111
+	for _, v := range h.Versions {
+		if !slices.Contains(allowedVersions, v) {
+			return fmt.Errorf("unsupported HTTP version: %s, supported version: %s", v, allowedVersionsString)
+		}
+	}
 
 	rt, err := h.NewTransport(ctx)
 	if err != nil {