diff --git a/certdb/sql/database_accessor.go b/certdb/sql/database_accessor.go
index 63b0db8bf..d9ff78198 100644
--- a/certdb/sql/database_accessor.go
+++ b/certdb/sql/database_accessor.go
@@ -3,10 +3,13 @@ package sql
 import (
 	"errors"
 	"fmt"
+	"regexp"
 	"time"
 
 	"github.com/cloudflare/cfssl/certdb"
 	cferr "github.com/cloudflare/cfssl/errors"
+	"github.com/go-sql-driver/mysql"
+	"github.com/mattn/go-sqlite3"
 
 	"github.com/jmoiron/sqlx"
 	"github.com/kisielk/sqlstruct"
@@ -76,7 +79,37 @@ var _ certdb.Accessor = &Accessor{}
 
 func wrapSQLError(err error) error {
 	if err != nil {
-		return cferr.Wrap(cferr.CertStoreError, cferr.Unknown, err)
+
+		reason := cferr.Unknown
+
+		// Use detailed reason on unique constraint errors (i.e. will allow API client
+		// to detect already used cert serial in DB when API client is
+		// allowed to provide cert serial on cert singing). We don't detect this
+		// kind of problems by querying table for exisitng key before insert/update
+		// to avoid races. Unique constraint errors have different codes in different
+		// DB engines so must be detected separately.
+
+		// MySQL/MariaDB
+		var mysqlErr *mysql.MySQLError
+		if errors.As(err, &mysqlErr) && mysqlErr.Number == 1062 {
+			reason = cferr.DuplicateEntry
+		}
+
+		// SQLite
+		var sqliteErr sqlite3.Error
+		if errors.As(err, &sqliteErr) && (sqliteErr.Code == sqlite3.ErrConstraint) {
+
+			// Parsing error message is probably the only way to detect duplicate key
+			// errors in SQLite now...
+			if regexp.MustCompile(`(^|\s)UNIQUE constraint failed .*`).MatchString(err.Error()) {
+				reason = cferr.DuplicateEntry
+			}
+		}
+
+		// PostgresSQL
+		// TBD. See also: https://github.com/go-gorm/gorm/issues/4135
+
+		return cferr.Wrap(cferr.CertStoreError, reason, err)
 	}
 	return nil
 }
diff --git a/config/config.go b/config/config.go
index f97d64698..36baf10a5 100644
--- a/config/config.go
+++ b/config/config.go
@@ -19,6 +19,7 @@ import (
 	"github.com/cloudflare/cfssl/helpers"
 	"github.com/cloudflare/cfssl/log"
 	ocspConfig "github.com/cloudflare/cfssl/ocsp/config"
+
 	// empty import of zlint/v3 required to have lints registered.
 	_ "github.com/zmap/zlint/v3"
 	"github.com/zmap/zlint/v3/lint"
@@ -121,7 +122,7 @@ type SigningProfile struct {
 	CSRWhitelist                *CSRWhitelist
 	NameWhitelist               *regexp.Regexp
 	ExtensionWhitelist          map[string]bool
-	ClientProvidesSerialNumbers bool
+	ClientProvidesSerialNumbers bool `json:"client_provides_serial_numbers"`
 	// LintRegistry is the collection of lints that should be used if
 	// LintErrLevel is configured. By default all ZLint lints are used. If
 	// ExcludeLints or ExcludeLintSources are set then this registry will be
diff --git a/errors/error.go b/errors/error.go
index 9715a7cfb..3a3f1573d 100644
--- a/errors/error.go
+++ b/errors/error.go
@@ -210,6 +210,9 @@ const (
 	// RecordNotFound occurs when a SQL query targeting on one unique
 	// record failes to update the specified row in the table.
 	RecordNotFound
+	// DuplicateEntry occurs when SQL query tries to insert or update
+	// using key that must be unique in db table but already exists there.
+	DuplicateEntry
 )
 
 // The error interface implementation, which formats to a JSON object string.