diff --git a/flang/lib/Parser/basic-parsers.h b/flang/lib/Parser/basic-parsers.h
--- a/flang/lib/Parser/basic-parsers.h
+++ b/flang/lib/Parser/basic-parsers.h
@@ -729,13 +729,7 @@
       return RESULT{};
     } else {
       if constexpr (sizeof...(PARSER) == 1) {
-        if constexpr (std::is_same_v<Success, typename PARSER::resultType...>) {
-          if (std::get<0>(parsers_).Parse(state)) {
-            return RESULT{};
-          }
-        } else if (auto arg{std::get<0>(parsers_).Parse(state)}) {
-          return RESULT{std::move(*arg)};
-        }
+        return ParseOne(state);
       } else {
         ApplyArgs<PARSER...> results;
         using Sequence = std::index_sequence_for<PARSER...>;
@@ -749,6 +743,17 @@
   }
 
 private:
+  std::optional<resultType> ParseOne(ParseState &state) const {
+    if constexpr (std::is_same_v<Success, typename PARSER::resultType...>) {
+      if (std::get<0>(parsers_).Parse(state)) {
+        return RESULT{};
+      }
+    } else if (auto arg{std::get<0>(parsers_).Parse(state)}) {
+      return RESULT{std::move(*arg)};
+    }
+    return std::nullopt;
+  }
+
   const std::tuple<PARSER...> parsers_;
 };