diff --git a/go/libraries/doltcore/table/untyped/csv/writer.go b/go/libraries/doltcore/table/untyped/csv/writer.go
index 8fd56e19f57..0781d6608fd 100644
--- a/go/libraries/doltcore/table/untyped/csv/writer.go
+++ b/go/libraries/doltcore/table/untyped/csv/writer.go
@@ -126,19 +126,17 @@ func (csvw *CSVWriter) WriteSqlRow(ctx *sql.Context, r sql.Row) error {
 }
 
 func toCsvString(ctx *sql.Context, colType sql.Type, val interface{}) (string, error) {
-	var v string
-	// Due to BIT's unique output, we special-case writing the integer specifically for CSV
+	// For BIT, emit base-10 int, instead of bytes
 	if _, ok := colType.(types.BitType); ok {
-		v = strconv.FormatUint(val.(uint64), 10)
-	} else {
-		var err error
-		v, err = sqlutil.SqlColToStr(ctx, colType, val)
+		// Normalize to handle UNION type generalization (e.g., int64 -> uint64)
+		norm, _, err := colType.Convert(ctx, val)
 		if err != nil {
 			return "", err
 		}
+		return strconv.FormatUint(norm.(uint64), 10), nil
 	}
 
-	return v, nil
+	return sqlutil.SqlColToStr(ctx, colType, val)
 }
 
 func (csvw *CSVWriter) processRowWithSchema(r sql.Row, ctx *sql.Context) ([]*string, error) {
diff --git a/integration-tests/bats/sql-export.bats b/integration-tests/bats/sql-export.bats
index 2061e74642e..001cdd89196 100644
--- a/integration-tests/bats/sql-export.bats
+++ b/integration-tests/bats/sql-export.bats
@@ -101,3 +101,11 @@ teardown() {
     [ "$status" -eq 1 ]
     [[ "$output" =~ "Result consisted of more than one row" ]] || false
 }
+
+@test "sql-export: bit union csv output regression test for dolt#9641" {
+    dolt sql -q "CREATE TABLE collection (id INT, archived BIT(1));"
+    dolt sql -q "INSERT INTO collection VALUES (1, b'0'), (2, b'0');"
+    run dolt sql --result-format=csv -q "SELECT * FROM (SELECT archived FROM collection WHERE archived = FALSE UNION ALL SELECT NULL AS archived FROM collection WHERE id = 1) AS dummy_alias;"
+    [ "$status" -eq 0 ]
+    [[ "$output" =~ "archived" ]] || false
+}