diff --git a/knx/cemi/address.go b/knx/cemi/address.go
index a79d3da..565ff58 100644
--- a/knx/cemi/address.go
+++ b/knx/cemi/address.go
@@ -96,11 +96,11 @@ func NewGroupAddr3(a, b, c uint8) GroupAddr {
 	return GroupAddr(a&0x1F)<<11 | GroupAddr(b&0x7)<<8 | GroupAddr(c)
 }
 
-// NewGroupAddr2 generates a group address from and "a/b"
+// NewGroupAddr2 generates a group address from an "a/b"
 // representation, where a is the Main Group [0..31] and b is
 // the Sub Group [0..2047].
 func NewGroupAddr2(a uint8, b uint16) GroupAddr {
-	return GroupAddr(a)<<8 | GroupAddr(b&0x7FF)
+	return GroupAddr(a&0x1F)<<11 | GroupAddr(b&0x7FF)
 }
 
 // NewGroupAddrString parses the given string to a group address.
diff --git a/knx/cemi/address_test.go b/knx/cemi/address_test.go
index 16f6fe9..e511a36 100644
--- a/knx/cemi/address_test.go
+++ b/knx/cemi/address_test.go
@@ -64,7 +64,8 @@ func Test_GroupAddresses(t *testing.T) {
 	var addrs = []Addr{
 		{"1/2/3", true, "1/2/3"},
 		{"31/7/255", true, "31/7/255"},
-		{"31/2040", true, "3/7/248"},
+		{"31/2040", true, "31/7/248"},
+		{"31/2047", true, "31/7/255"},
 		{"65535", true, "31/7/255"},
 		{"82/8/260", false, ""},
 		{"84/230", false, ""},