WDK fltKernel.h C4324 error under /W4 /WX — VS2026

No Microsoft-published SDK/toolset correction or official fltkernel.h fix for C4324 is currently identified in WDK 28000.2526; with suppression and layout changes excluded, submit a minimal reproducer through Visual Studio’s Report a Problem and track it until Microsoft identifies a fixed release.

WDK 28000.2526 with Visual Studio 2026 is the current supported combination, so moving to VS 2022 is not the designated correction for this case.^1^ ^2^

Current status

• Microsoft documents C4324 as indicating that padding was added because an alignment specifier requires alignment greater than the type’s natural alignment.^3^
• The published FLT_PARAMETERS definition intentionally contains POINTER_ALIGNMENT on members including FileAttributes, EaLength, and numerous other fields.^4^
• The WDK 28000.2526 release notes do not list a correction to fltkernel.h or C4324. Their documented impacted headers concern Wi-Fi, StorPort, and NVMe ICE changes.^5^
• C2220 is the consequence of /WX promoting the preceding warning to an error; investigate and report the first C4324 diagnostic rather than C2220.

Accordingly, there is no documented drop-in header or toolset update that can presently satisfy all of these requirements simultaneously:

• retain /W4 /WX;
• avoid warning suppression;
• leave WDK headers unchanged;
• preserve packing, alignment, layout, and ABI.

Do not remove POINTER_ALIGNMENT, edit fltkernel.h, or introduce packing pragmas. Microsoft’s driver guidance cautions against changing packing levels because misalignment can produce platform-specific failures.^6^

Verify the supported installation before filing

The SDK and WDK build numbers must match; QFE values only need to match when later-QFE header functionality is required.^1^

1. Open Windows Settings → Apps → Installed apps.
2. Search for kit.
3. Confirm that both SDK and WDK report build 28000. Do not rely solely on the Windows Kits\10\Include\10.0.28000.0 directory because its QFE component is hardcoded and is not a reliable installed-QFE indicator.
4. Open the VS 2026 developer command prompt and capture the compiler version:

cl /Bv

5. Rebuild with detailed MSBuild output and retain the complete first C4324 diagnostic, target architecture, and compiler command line.

Submit the correction request

In Visual Studio, select:

Help → Send Feedback → Report a Problem

Search first for an existing fltKernel.h C4324 POINTER_ALIGNMENT report. If one exists, vote for it and attach your exact version and reproduction details; otherwise select Can’t find the solution and submit a new ticket. Reports submitted through Visual Studio can include diagnostics and are routed into Microsoft’s engineering system.^7^

Include:

• full cl /Bv output;
• VS 2026 version and edition;
• SDK and WDK full versions;
• target architecture;
• complete cl.exe command line, preferably from CL.command.1.tlog;
• the first C4324 message and subsequent C2220;
• a minimal source file that includes fltKernel.h;
• confirmation that /W4 /WX is required and that suppression, header edits, and packing/alignment changes are unacceptable.

Microsoft’s C++ reporting guidance specifically requests the complete toolset version, compiler command line, exact diagnostics, and a minimal self-contained reproducer.^8^

A Developer Community item marked Fixed – Pending Release or Closed – Fixed, with a stated “fixed in” version, is the appropriate confirmation that a compatible compiler or WDK correction is available.^7^

References

1. Download the Windows Driver Kit (WDK)
2. Supported WDK versions
3. Compiler Warning (level 4) C4324
4. FLT_PARAMETERS (fltkernel.h) - Windows drivers | Microsoft Learn
5. Windows Driver Kit (WDK) release notes
6. Porting Issues Checklist
7. Report a problem with the Visual Studio product or installer
8. How to report a problem with the Microsoft C++ Build Tools or documentation