diff --git a/src/lib/fmt/Unsafe.hxx b/src/lib/fmt/Unsafe.hxx
new file mode 100644
index 000000000..373b39e7b
--- /dev/null
+++ b/src/lib/fmt/Unsafe.hxx
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: BSD-2-Clause
+// author: Max Kellermann <max.kellermann@gmail.com>
+
+#pragma once
+
+#include <fmt/core.h>
+
+#include <string_view>
+
+/**
+ * Format without bounds checking and return a C string.
+ */
+[[nodiscard]]
+inline const char *
+VFmtUnsafeC(char *dest, fmt::string_view format_str, fmt::format_args args) noexcept
+{
+	*fmt::vformat_to(dest, format_str, args) = '\0';
+	return dest;
+}
+
+template<typename S, typename... Args>
+[[nodiscard]]
+constexpr const char *
+FmtUnsafeC(char *dest, const S &format_str, Args&&... args) noexcept
+{
+	return VFmtUnsafeC(dest, format_str, fmt::make_format_args(args...));
+}
+
+/**
+ * Format without bounds checking and return a std::string_view.
+ */
+[[nodiscard]]
+inline std::string_view
+VFmtUnsafeSV(char *dest, fmt::string_view format_str, fmt::format_args args) noexcept
+{
+	return {dest, fmt::vformat_to(dest, format_str, args)};
+}
+
+template<typename S, typename... Args>
+[[nodiscard]]
+std::string_view
+FmtUnsafeSV(char *dest, const S &format_str, Args&&... args) noexcept
+{
+	return VFmtUnsafeSV(dest, format_str, fmt::make_format_args(args...));
+}