diff --git a/wei.go b/wei.go
index df00f41..4b0c347 100644
--- a/wei.go
+++ b/wei.go
@@ -4,11 +4,10 @@ import (
 	"math/big"
 )
 
-// ConvertToWei deprecated. Instead of ConvertToWei just use decimal.ToBig()
 func ConvertToWei(dec *Decimal, mantissa uint8) *big.Int {
 	if dec == nil || dec.value == nil {
 		return new(big.Int).SetUint64(0)
 	}
 
-	return NewDecimal(dec).ToBig()
+	return NewDecimal(dec).Rescale(mantissa).ToBig()
 }
diff --git a/wei_test.go b/wei_test.go
index 0b86617..c608693 100644
--- a/wei_test.go
+++ b/wei_test.go
@@ -7,40 +7,53 @@ import (
 )
 
 func TestConvertToWei(t *testing.T) {
-	d, ok := NewDecimalFromString("1")
+	actual, ok := NewDecimalFromString("1")
 	assert.True(t, ok)
-	assert.Equal(t, ConvertToWei(d, 0), new(big.Int).SetUint64(1))
+	assert.Equal(t, new(big.Int).SetUint64(1), ConvertToWei(actual, 0))
 
-	d, ok = NewDecimalFromString("1")
+	actual, ok = NewDecimalFromString("1")
 	assert.True(t, ok)
-	assert.Equal(t, ConvertToWei(d, 10), new(big.Int).SetUint64(1))
+	assert.Equal(t, new(big.Int).SetUint64(10000000000), ConvertToWei(actual, 10))
 
-	d, ok = NewDecimalFromString("999999999999999999")
+	actual, ok = NewDecimalFromString("999999999999999999")
 	assert.True(t, ok)
-	assert.Equal(t, ConvertToWei(d, 10), new(big.Int).SetUint64(999999999999999999))
+	expected, ok := new(big.Int).SetString("9999999999999999990000000000", 10)
+	assert.True(t, ok)
+	assert.Equal(t, expected, ConvertToWei(actual, 10))
 
-	d, ok = NewDecimalFromString("115792089237316195423570985008687907853269984665640564039457584007913129639935")
+	actual, ok = NewDecimalFromString("115792089237316195423570985008687907853269984665640564039457584007913129639935")
+	assert.True(t, ok)
+	expected, ok = new(big.Int).SetString("115792089237316195423570985008687907853269984665640564039457584007913129639935", 10)
 	assert.True(t, ok)
-	expected, ok := new(big.Int).SetString("115792089237316195423570985008687907853269984665640564039457584007913129639935", 10)
-	assert.Equal(t, ConvertToWei(d, 0), expected)
+	assert.Equal(t, expected, ConvertToWei(actual, 0))
 
-	d, ok = NewDecimalFromString("115792089237316195423570985008687907853269984665640564039457584007913129639935")
+	actual, ok = NewDecimalFromString("115792089237316195423570985008687907853269984665640564039457584007913129639935")
 	assert.True(t, ok)
 	expected, ok = new(big.Int).SetString("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 16)
-	assert.Equal(t, ConvertToWei(d, 0), expected)
+	assert.True(t, ok)
+	assert.Equal(t, expected, ConvertToWei(actual, 0))
 
-	d, ok = NewDecimalFromString("10.10001")
+	actual, ok = NewDecimalFromString("10.10001")
 	assert.True(t, ok)
 	expected, ok = new(big.Int).SetString("1010001", 10)
-	assert.Equal(t, ConvertToWei(d, 0), expected)
+	assert.True(t, ok)
+	assert.Equal(t, expected, ConvertToWei(actual, 5))
 
-	d, ok = NewDecimalFromString("10.10001111111999999999901")
+	actual, ok = NewDecimalFromString("10.10001111111999999999901")
 	assert.True(t, ok)
 	expected, ok = new(big.Int).SetString("1010001111111999999999901", 10)
-	assert.Equal(t, ConvertToWei(d, 0), expected)
+	assert.True(t, ok)
+	assert.Equal(t, expected, ConvertToWei(actual, 23))
 
-	d, ok = NewDecimalFromString("10.1000111111199999999990112312313123123123")
+	actual, ok = NewDecimalFromString("10.1000111111199999999990112312313123123123")
 	assert.True(t, ok)
 	expected, ok = new(big.Int).SetString("101000111111199999999990112312313123123123", 10)
-	assert.Equal(t, ConvertToWei(d, 0), expected)
+	assert.True(t, ok)
+	assert.Equal(t, expected, ConvertToWei(actual, 40))
+
+	actual, ok = NewDecimalFromString("115792089237316195423570985008687907853269984665640564039457.584007913129639935")
+	assert.True(t, ok)
+	expected, ok = new(big.Int).SetString("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 16)
+	assert.True(t, ok)
+	assert.Equal(t, expected, ConvertToWei(actual, 18))
 }