diff --git a/include/etl/format.h b/include/etl/format.h
index 8820ac6f..830e64a6 100644
--- a/include/etl/format.h
+++ b/include/etl/format.h
@@ -35,7 +35,6 @@ SOFTWARE.
 
 #include "algorithm.h"
 #include "array.h"
-#include "array_view.h"
 #include "error_handler.h"
 #include "limits.h"
 #include "math.h"
@@ -627,7 +626,7 @@ namespace etl
     };
 
     template <typename T>
-    struct has_formatter_parse<T, etl::void_t<decltype(etl::declval<etl::formatter<T>&>().parse(etl::declval<format_parse_context&>()))> >
+    struct has_formatter_parse<T, etl::void_t<decltype(etl::declval<etl::formatter<T>&>().parse(etl::declval<format_parse_context&>()))>>
       : etl::true_type
     {
     };
@@ -642,7 +641,7 @@ namespace etl
 
     template <typename T>
     struct has_formatter_format<T, etl::void_t<decltype(etl::declval<etl::formatter<T>&>().format(
-                                     etl::declval<const T&>(), etl::declval<etl::basic_format_context<char*, char>&>()))> > : etl::true_type
+                                     etl::declval<const T&>(), etl::declval<etl::basic_format_context<char*, char>&>()))>> : etl::true_type
     {
     };
 
@@ -806,7 +805,7 @@ namespace etl
     // Converting constructor for user-defined types that provide an
     // etl::formatter<T> specialisation. The value is stored type-erased in a
     // handle, matching the std::basic_format_arg behaviour for custom types.
-    template <typename T, typename = etl::enable_if_t<private_format::is_formattable<T>::value> >
+    template <typename T, typename = etl::enable_if_t<private_format::is_formattable<T>::value>>
     basic_format_arg(const T& v)
       : data(handle(v))
     {
@@ -863,7 +862,7 @@ namespace etl
       return _args.get(i);
     }
 
-    etl::array_view<basic_format_arg<Context>> get()
+    etl::span<basic_format_arg<Context>> get()
     {
       return _args;
     }
@@ -884,6 +883,15 @@ namespace etl
     {
     }
 
+    // non-standard
+    // Constructs from externally owned storage, for cases where the number of
+    // arguments is only known at runtime and so no format_arg_store<Context, Args...>
+    // can be formed. The referenced storage must outlive this object.
+    explicit basic_format_args(etl::span<basic_format_arg<Context>> args_)
+      : _args(args_)
+    {
+    }
+
     basic_format_args(const basic_format_args<Context>& other)
       : _args(other._args)
     {
@@ -908,7 +916,7 @@ namespace etl
 
   private:
 
-    etl::array_view<basic_format_arg<Context>> _args;
+    etl::span<basic_format_arg<Context>> _args;
   };
 
   namespace private_format
@@ -2019,7 +2027,7 @@ namespace etl
       }
 
       // for user-defined types routed through basic_format_arg::handle
-      void operator()(typename basic_format_arg<format_context<OutputIt> >::handle h)
+      void operator()(typename basic_format_arg<format_context<OutputIt>>::handle h)
       {
         h.format(parse_ctx, fmt_ctx);
       }
diff --git a/test/test_format.cpp b/test/test_format.cpp
index 480345b5..bfd4c848 100644
--- a/test/test_format.cpp
+++ b/test/test_format.cpp
@@ -950,6 +950,29 @@ namespace
       CHECK_EQUAL("010", test_format(s, "{:#o}", 8));
     }
 
+    //*************************************************************************
+    // Arguments whose count is only known at runtime cannot be held in a
+    // format_arg_store<Context, Args...>, so basic_format_args can also be built
+    // directly over caller owned storage.
+    TEST(test_vformat_to_runtime_sized_args)
+    {
+      etl::string<100> s;
+
+      using iterator_t = etl::back_insert_iterator<etl::string<100>>;
+      using arg_t      = etl::format_arg<iterator_t>;
+
+      etl::array<arg_t, 4> storage = {arg_t(1), arg_t("two"), arg_t(3), arg_t('x')};
+
+      // Only the first three of the four slots are used.
+      etl::vformat_to(etl::back_inserter(s), "{} {} {}", etl::format_args<iterator_t>(etl::span<arg_t>(storage.data(), 3U)));
+      CHECK_EQUAL("1 two 3", s);
+
+      // An empty argument list is also valid.
+      s.clear();
+      etl::vformat_to(etl::back_inserter(s), "no args", etl::format_args<iterator_t>(etl::span<arg_t>()));
+      CHECK_EQUAL("no args", s);
+    }
+
     //*************************************************************************
     TEST(test_format_custom_type)
     {