How to fix Error 3804 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 3804 – Check Constraint Disabled Due to Checksum Function Change

Why This Error Happens

This warning occurs when a check constraint on a table uses the CHECKSUM() or BINARY_CHECKSUM() function, and the underlying implementation of that function has changed between SQL Server versions or builds (commonly after an in-place upgrade or cumulative update). Because the new checksum algorithm can produce different hash values than the one originally used to validate existing data, SQL Server automatically disables the constraint rather than risk incorrectly flagging valid rows as violations. This is a protective mechanism, not data corruption, but it means the constraint is no longer being enforced until it is manually rebuilt and revalidated.

Step-by-Step Resolution Guide

Step 1: Identify the Affected Constraint and Table

  • Run the following query to confirm which constraints are disabled and reference checksum logic:
SELECT name, OBJECT_NAME(parent_object_id) AS TableName, definition
FROM sys.check_constraints
WHERE is_disabled = 1;
  • Review the definition column for any use of CHECKSUM(*) or BINARY_CHECKSUM(*).
  • Note the exact table name and schema reported in the Error 3804 message text.

Step 2: Drop and Recreate the Check Constraint

  • Script out the existing constraint definition before dropping it (use SSMS “Script Constraint as DROP and CREATE To” for safety).
  • Drop the disabled constraint:
ALTER TABLE dbo.YourTable
DROP CONSTRAINT CK_YourConstraintName;
  • Recreate it using the same logical checksum validation, forcing SQL Server to recalculate it with the current engine version:
ALTER TABLE dbo.YourTable
ADD CONSTRAINT CK_YourConstraintName
CHECK (CHECKSUM(ColumnA, ColumnB) <> 0);

Step 3: Validate Existing Data Against the New Constraint

  • Use WITH CHECK explicitly to force SQL Server to re-verify all existing rows against the new checksum logic rather than trusting old values:
ALTER TABLE dbo.YourTable WITH CHECK
CHECK CONSTRAINT CK_YourConstraintName;
  • If this fails, identify non-conforming rows first using a SELECT with the same CHECK expression negated, then clean the data before re-enabling.

Step 4: Apply Latest Cumulative Update (CU) Consistently Across Nodes

  • On Windows Server 2025 clusters or Always On Availability Groups, ensure all replicas are running the identical SQL Server 2025 build to avoid checksum mismatches between nodes.
  • Verify current build via:
SELECT @@VERSION;
  • Download and apply the matching CU from the Microsoft Update Catalog if versions differ across nodes.

Alternative or Verification Steps

  • Confirm the fix by re-running the sys.check_constraints query from Step 1 — the is_disabled column should now return 0 for the affected constraint.
  • If rebuilding the constraint is not immediately feasible, temporarily document and monitor the table at the application layer, then schedule a maintenance window to run DBCC CHECKCONSTRAINTS('YourTable') to confirm data integrity before re-enabling enforcement.