2 files changed, 29 insertions, 1 deletions
diff --git a/src/database/sql/driver/types.go b/src/database/sql/driver/types.go
index 64b41faaa8..24c3a45483 100644
--- a/src/database/sql/driver/types.go
+++ b/src/database/sql/driver/types.go
@@ -180,6 +180,8 @@ func IsValue(v interface{}) bool {
 	switch v.(type) {
 	case []byte, bool, float64, int64, string, time.Time:
 		return true
+	case decimalDecompose:
+		return true
 	}
 	return false
 }
@@ -236,7 +238,8 @@ func (defaultConverter) ConvertValue(v interface{}) (Value, error) {
 		return v, nil
 	}
 
-	if vr, ok := v.(Valuer); ok {
+	switch vr := v.(type) {
+	case Valuer:
 		sv, err := callValuerValue(vr)
 		if err != nil {
 			return nil, err
@@ -245,6 +248,10 @@ func (defaultConverter) ConvertValue(v interface{}) (Value, error) {
 			return nil, fmt.Errorf("non-Value type %T returned from Value", sv)
 		}
 		return sv, nil
+
+	// For now, continue to prefer the Valuer interface over the decimal decompose interface.
+	case decimalDecompose:
+		return vr, nil
 	}
 
 	rv := reflect.ValueOf(v)
@@ -281,3 +288,10 @@ func (defaultConverter) ConvertValue(v interface{}) (Value, error) {
 	}
 	return nil, fmt.Errorf("unsupported type %T, a %s", v, rv.Kind())
 }
+
+type decimalDecompose interface {
+	// Decompose returns the internal decimal state into parts.
+	// If the provided buf has sufficient capacity, buf may be returned as the coefficient with
+	// the value set and length set as appropriate.
+	Decompose(buf []byte) (form byte, negative bool, coefficient []byte, exponent int32)
+}
diff --git a/src/database/sql/driver/types_test.go b/src/database/sql/driver/types_test.go
index 0379bf8892..4c2996da85 100644
--- a/src/database/sql/driver/types_test.go
+++ b/src/database/sql/driver/types_test.go
@@ -57,6 +57,7 @@ var valueConverterTests = []valueConverterTest{
 	{DefaultParameterConverter, bs{1}, []byte{1}, ""},
 	{DefaultParameterConverter, s("a"), "a", ""},
 	{DefaultParameterConverter, is{1}, nil, "unsupported type driver.is, a slice of int"},
+	{DefaultParameterConverter, dec{exponent: -6}, dec{exponent: -6}, ""},
 }
 
 func TestValueConverters(t *testing.T) {
@@ -79,3 +80,16 @@ func TestValueConverters(t *testing.T) {
 		}
 	}
 }
+
+type dec struct {
+	form        byte
+	neg         bool
+	coefficient [16]byte
+	exponent    int32
+}
+
+func (d dec) Decompose(buf []byte) (form byte, negative bool, coefficient []byte, exponent int32) {
+	coef := make([]byte, 16)
+	copy(coef, d.coefficient[:])
+	return d.form, d.neg, coef, d.exponent
+}