diff --git a/pkg/templates/template_funcs.go b/pkg/templates/template_funcs.go
index edf61d8..f653d48 100644
--- a/pkg/templates/template_funcs.go
+++ b/pkg/templates/template_funcs.go
@@ -188,7 +188,11 @@ func UrlEncode(values ...interface{}) string {
 func QueryPlus(r *http.Request) func(...interface{}) template.URL {
 	return func(upsert ...interface{}) template.URL {
 		// Get current parameters.
-		var params = r.Form
+		// Note: COPY them from r.Form so we don't accidentally modify r.Form.
+		var params = map[string][]string{}
+		for k, v := range r.Form {
+			params[k] = v
+		}
 
 		// Mix in the incoming fields.
 		for i := 0; i < len(upsert); i += 2 {