diff --git a/src/database/sql/convert.go b/src/database/sql/convert.go
index 7a3b5fa..4c056a1 100644
--- a/src/database/sql/convert.go
+++ b/src/database/sql/convert.go
@@ -288,6 +288,11 @@
 			*d = s.AppendFormat((*d)[:0], time.RFC3339Nano)
 			return nil
 		}
+	case decimalDecompose:
+		switch d := dest.(type) {
+		case decimalCompose:
+			return d.Compose(s.Decompose(nil))
+		}
 	case nil:
 		switch d := dest.(type) {
 		case *interface{}:
@@ -553,3 +558,42 @@
 	}
 	return vr.Value()
 }
+
+// decimal composes or decomposes a decimal value to and from individual parts.
+// There are four parts: a boolean negative flag, a form byte with three possible states
+// (finite=0, infinite=1, NaN=2), a base-2 big-endian integer
+// coefficient (also known as a significand) as a []byte, and an int32 exponent.
+// These are composed into a final value as "decimal = (neg) (form=finite) coefficient * 10 ^ exponent".
+// A zero length coefficient is a zero value.
+// The big-endian integer coefficent stores the most significant byte first (at coefficent[0]).
+// If the form is not finite the coefficient and exponent should be ignored.
+// The negative parameter may be set to true for any form, although implementations are not required
+// to respect the negative parameter in the non-finite form.
+//
+// Implementations may choose to set the negative parameter to true on a zero or NaN value,
+// but implementations that do not differentiate between negative and positive
+// zero or NaN values should ignore the negative parameter without error.
+// If an implementation does not support Infinity it may be converted into a NaN without error.
+// If a value is set that is larger than what is supported by an implementation,
+// an error must be returned.
+// Implementations must return an error if a NaN or Infinity is attempted to be set while neither
+// are supported.
+//
+// NOTE(kardianos): This is an experimental interface. See https://golang.org/issue/30870
+type decimal interface {
+	decimalDecompose
+	decimalCompose
+}
+
+type decimalDecompose interface {
+	// Decompose returns the internal decimal state in 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)
+}
+
+type decimalCompose interface {
+	// Compose sets the internal decimal value from parts. If the value cannot be
+	// represented then an error should be returned.
+	Compose(form byte, negative bool, coefficient []byte, exponent int32) error
+}
diff --git a/src/database/sql/convert_test.go b/src/database/sql/convert_test.go
index 412f0b1..8a82891 100644
--- a/src/database/sql/convert_test.go
+++ b/src/database/sql/convert_test.go
@@ -494,3 +494,107 @@
 		}
 	}
 }
+
+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
+}
+
+func (d *dec) Compose(form byte, negative bool, coefficient []byte, exponent int32) error {
+	switch form {
+	default:
+		return fmt.Errorf("unknown form %d", form)
+	case 1, 2:
+		d.form = form
+		d.neg = negative
+		return nil
+	case 0:
+	}
+	d.form = form
+	d.neg = negative
+	d.exponent = exponent
+
+	// This isn't strictly correct, as the extra bytes could be all zero,
+	// ignore this for this test.
+	if len(coefficient) > 16 {
+		return fmt.Errorf("coefficent too large")
+	}
+	copy(d.coefficient[:], coefficient)
+
+	return nil
+}
+
+type decFinite struct {
+	neg         bool
+	coefficient [16]byte
+	exponent    int32
+}
+
+func (d decFinite) Decompose(buf []byte) (form byte, negative bool, coefficient []byte, exponent int32) {
+	coef := make([]byte, 16)
+	copy(coef, d.coefficient[:])
+	return 0, d.neg, coef, d.exponent
+}
+
+func (d *decFinite) Compose(form byte, negative bool, coefficient []byte, exponent int32) error {
+	switch form {
+	default:
+		return fmt.Errorf("unknown form %d", form)
+	case 1, 2:
+		return fmt.Errorf("unsupported form %d", form)
+	case 0:
+	}
+	d.neg = negative
+	d.exponent = exponent
+
+	// This isn't strictly correct, as the extra bytes could be all zero,
+	// ignore this for this test.
+	if len(coefficient) > 16 {
+		return fmt.Errorf("coefficent too large")
+	}
+	copy(d.coefficient[:], coefficient)
+
+	return nil
+}
+
+func TestDecimal(t *testing.T) {
+	list := []struct {
+		name string
+		in   decimalDecompose
+		out  dec
+		err  bool
+	}{
+		{name: "same", in: dec{exponent: -6}, out: dec{exponent: -6}},
+
+		// Ensure reflection is not used to assign the value by using different types.
+		{name: "diff", in: decFinite{exponent: -6}, out: dec{exponent: -6}},
+
+		{name: "bad-form", in: dec{form: 200}, err: true},
+	}
+	for _, item := range list {
+		t.Run(item.name, func(t *testing.T) {
+			out := dec{}
+			err := convertAssign(&out, item.in)
+			if item.err {
+				if err == nil {
+					t.Fatalf("unexpected nil error")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if !reflect.DeepEqual(out, item.out) {
+				t.Fatalf("got %#v want %#v", out, item.out)
+			}
+		})
+	}
+}
diff --git a/src/database/sql/driver/types.go b/src/database/sql/driver/types.go
index 64b41fa..24c3a45 100644
--- a/src/database/sql/driver/types.go
+++ b/src/database/sql/driver/types.go
@@ -180,6 +180,8 @@
 	switch v.(type) {
 	case []byte, bool, float64, int64, string, time.Time:
 		return true
+	case decimalDecompose:
+		return true
 	}
 	return false
 }
@@ -236,7 +238,8 @@
 		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 @@
 			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 @@
 	}
 	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 0379bf8..4c2996d 100644
--- a/src/database/sql/driver/types_test.go
+++ b/src/database/sql/driver/types_test.go
@@ -57,6 +57,7 @@
 	{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 @@
 		}
 	}
 }
+
+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
+}
diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index a95b70c..f68cefe 100644
--- a/src/database/sql/sql_test.go
+++ b/src/database/sql/sql_test.go
@@ -3606,7 +3606,7 @@
 	skipNamedValueCheck bool
 }
 
-type decimal struct {
+type decimalInt struct {
 	value int
 }
 
@@ -3630,7 +3630,7 @@
 			nv.Value = "OUT:*string"
 		}
 		return nil
-	case decimal, []int64:
+	case decimalInt, []int64:
 		return nil
 	case doNotInclude:
 		return driver.ErrRemoveArgument
@@ -3659,13 +3659,13 @@
 	}
 
 	o1 := ""
-	_, err = db.ExecContext(ctx, "INSERT|keys|dec1=?A,str1=?,out1=?O1,array1=?", Named("A", decimal{123}), "hello", Named("O1", Out{Dest: &o1}), []int64{42, 128, 707}, doNotInclude{})
+	_, err = db.ExecContext(ctx, "INSERT|keys|dec1=?A,str1=?,out1=?O1,array1=?", Named("A", decimalInt{123}), "hello", Named("O1", Out{Dest: &o1}), []int64{42, 128, 707}, doNotInclude{})
 	if err != nil {
 		t.Fatal("exec insert", err)
 	}
 	var (
 		str1 string
-		dec1 decimal
+		dec1 decimalInt
 		arr1 []int64
 	)
 	err = db.QueryRowContext(ctx, "SELECT|keys|dec1,str1,array1|").Scan(&dec1, &str1, &arr1)
@@ -3675,7 +3675,7 @@
 
 	list := []struct{ got, want interface{} }{
 		{o1, "from-server"},
-		{dec1, decimal{123}},
+		{dec1, decimalInt{123}},
 		{str1, "hello"},
 		{arr1, []int64{42, 128, 707}},
 	}
@@ -3708,7 +3708,7 @@
 		t.Fatal("exec create", err)
 	}
 
-	_, err = db.ExecContext(ctx, "INSERT|keys|dec1=?A", Named("A", decimal{123}))
+	_, err = db.ExecContext(ctx, "INSERT|keys|dec1=?A", Named("A", decimalInt{123}))
 	if err == nil {
 		t.Fatalf("expected error with bad argument, got %v", err)
 	}