One element multiple times

I want to be able to specify one element, in my case Param, multiple times. This is the XSD:

<xs:schema xmlns:xs="http://ift.tt/tphNwY">
    <xs:element name="Abc">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="Def" minOccurs="1" maxOccurs="unbounded">
                    <xs:complexType>
                        <xs:all>
                            <!-- ... other elements ... -->
                            <xs:element name="Param" minOccurs="0" maxOccurs="unbounded"> <!-- Using unbounded is not allowed here -->
                                <xs:complexType>
                                    <xs:attribute name="Name"/>
                                    <xs:attribute name="Value"/>
                                </xs:complexType>
                            </xs:element>
                            <!-- ... other elements ... -->
                        </xs:all>
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

This is the corresponding XML:

<Abc xsi:noNamespaceSchemaLocation="SourcesSchema.xsd" xmlns:xsi="http://ift.tt/ra1lAU">
    <Def>
        <Param Name="one" Value="blue"/>
        <Param Name="two" Value="yellow"/>
        <Param Name="three" Value="green"/>
    </Def >
</Abc>

Trying this, I get the following exception:

Cos-all-limited.2: The {max Occurs} Of An Element In An 'all' Model Group Must Be 0 Or 1. The Value '-1' For Element 'Param' Is Invalid.