diff --git a/src/lib/fmt/ToBuffer.hxx b/src/lib/fmt/ToBuffer.hxx
new file mode 100644
index 000000000..5ba36c068
--- /dev/null
+++ b/src/lib/fmt/ToBuffer.hxx
@@ -0,0 +1,61 @@
+/*
+ * Copyright 2022 Max Kellermann <max.kellermann@gmail.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "util/StringBuffer.hxx"
+
+#include <fmt/core.h>
+
+template<std::size_t size>
+[[nodiscard]] [[gnu::pure]]
+auto
+VFmtBuffer(fmt::string_view format_str, fmt::format_args args) noexcept
+{
+	StringBuffer<size> buffer;
+	auto [p, _] = fmt::vformat_to_n(buffer.data(), buffer.capacity() - 1,
+					format_str, args);
+	*p = 0;
+	return buffer;
+}
+
+template<std::size_t size, typename S, typename... Args>
+[[nodiscard]] [[gnu::pure]]
+auto
+FmtBuffer(const S &format_str, Args&&... args) noexcept
+{
+#if FMT_VERSION >= 90000
+	return VFmtBuffer(format_str,
+			  fmt::make_format_args(args...));
+#else
+	return VFmtBuffer(fmt::to_string_view(format_str),
+			  fmt::make_args_checked<Args...>(format_str,
+							  args...));
+#endif
+}
diff --git a/src/system/FmtError.cxx b/src/system/FmtError.cxx
index 4ca2ddfc4..3645357bb 100644
--- a/src/system/FmtError.cxx
+++ b/src/system/FmtError.cxx
@@ -28,8 +28,7 @@
  */
 
 #include "FmtError.hxx"
-
-#include <fmt/format.h>
+#include "lib/fmt/ToBuffer.hxx"
 
 #include <array>
 
@@ -37,11 +36,8 @@ std::system_error
 VFmtSystemError(std::error_code code,
 		fmt::string_view format_str, fmt::format_args args) noexcept
 {
-	std::array<char, 512> buffer;
-	auto [p, _] = fmt::vformat_to_n(buffer.begin(), buffer.size() - 1,
-					format_str, args);
-	*p = 0;
-	return std::system_error{code, buffer.data()};
+	const auto msg = VFmtBuffer<512>(format_str, args);
+	return std::system_error{code, msg};
 }
 
 #ifdef _WIN32