diff --git a/ostd/format.hh b/ostd/format.hh
index 02968af..6c058f3 100644
--- a/ostd/format.hh
+++ b/ostd/format.hh
@@ -27,7 +27,7 @@ enum FormatFlags {
     FMT_FLAG_HASH  = 1 << 4
 };
 
-struct format_error: public std::runtime_error {
+struct format_error: std::runtime_error {
     using std::runtime_error::runtime_error;
 };
 
diff --git a/ostd/range.hh b/ostd/range.hh
index 6f90ed4..2f2f559 100644
--- a/ostd/range.hh
+++ b/ostd/range.hh
@@ -698,8 +698,10 @@ struct InputRange {
     }
 };
 
-template<typename R, typename F, typename = std::enable_if_t<IsInputRange<R>>>
-inline auto operator|(R &&range, F &&func) {
+template<typename R, typename F>
+inline auto operator|(R &&range, F &&func) ->
+    std::enable_if_t<IsInputRange<R>, decltype(func(std::forward<R>(range)))>
+{
     return func(std::forward<R>(range));
 }