diff --git a/src/win32/HResult.cxx b/src/win32/HResult.cxx
index 49e28db25..e81eb7c4a 100644
--- a/src/win32/HResult.cxx
+++ b/src/win32/HResult.cxx
@@ -26,9 +26,7 @@
 #include "system/Error.hxx"
 
 #include <cassert>
-#include <cstdarg>
 #include <cstdio>
-#include <memory>
 
 #include <combaseapi.h> // needed by audiopolicy.h if COM_NO_WINDOWS_H is defined
 #include <audiopolicy.h>
@@ -92,22 +90,3 @@ HResultCategory::message(int Errcode) const
 	assert(2 <= size && size <= 10);
 	return std::string(buffer, size);
 }
-
-std::system_error
-FormatHResultError(HRESULT result, const char *fmt, ...) noexcept
-{
-	std::va_list args1, args2;
-	va_start(args1, fmt);
-	va_copy(args2, args1);
-
-	const int size = vsnprintf(nullptr, 0, fmt, args1);
-	va_end(args1);
-	assert(size >= 0);
-
-	auto buffer = std::make_unique<char[]>(size + 1);
-	vsprintf(buffer.get(), fmt, args2);
-	va_end(args2);
-
-	return std::system_error(std::error_code(result, hresult_category()),
-				 std::string(buffer.get(), size));
-}
diff --git a/src/win32/HResult.hxx b/src/win32/HResult.hxx
index 607c4ecf4..7ddec5138 100644
--- a/src/win32/HResult.hxx
+++ b/src/win32/HResult.hxx
@@ -52,7 +52,4 @@ MakeHResultError(HRESULT result, const char *msg) noexcept
 				 msg);
 }
 
-gcc_printf(2, 3) std::system_error
-FormatHResultError(HRESULT result, const char *fmt, ...) noexcept;
-
 #endif