diff --git a/tests/gsup/gsup_test.c b/tests/gsup/gsup_test.c
index 9712d77..0936893 100644
--- a/tests/gsup/gsup_test.c
+++ b/tests/gsup/gsup_test.c
@@ -217,6 +217,69 @@
 				0x02, 0x01, 0x47,
 	};
 
+	static const uint8_t send_mo_forward_sm_req[] = {
+		0x24, /* OSMO_GSUP_MSGT_MO_FORWARD_SM_REQUEST */
+		TEST_IMSI_IE,
+
+		/* SM related IEs */
+		0x40, 0x01, /* SM-RP-MR (Message Reference) */
+			0xfa,
+		0x41, 0x08, /* SM-RP-DA (Destination Address) */
+			0x03, /* SMSC address */
+				0x91, 0x52, 0x75, 0x47, 0x99, 0x09, 0x82,
+		0x42, 0x01, /* SM-RP-OA (Originating Address) */
+			0xff, /* Special case: noSM-RP-OA */
+		0x43, 0x04, /* SM-RP-UI (TPDU) */
+			0xde, 0xad, 0xbe, 0xef,
+	};
+
+	static const uint8_t send_mt_forward_sm_req[] = {
+		0x28, /* OSMO_GSUP_MSGT_MT_FORWARD_SM_REQUEST */
+		TEST_IMSI_IE,
+
+		/* SM related IEs */
+		0x40, 0x01, /* SM-RP-MR (Message Reference) */
+			0xfa,
+		0x41, 0x09, /* SM-RP-DA (Destination Address) */
+			0x01, /* IMSI */
+				0x21, 0x43, 0x65, 0x87, 0x09, 0x21, 0x43, 0xf5,
+		0x42, 0x08, /* SM-RP-OA (Originating Address) */
+			0x03, /* SMSC address */
+				0x91, 0x52, 0x75, 0x47, 0x99, 0x09, 0x82,
+		0x43, 0x04, /* SM-RP-UI (TPDU) */
+			0xde, 0xad, 0xbe, 0xef,
+		0x45, 0x01, /* SM-RP-MMS (More Messages to Send) */
+			0x01,
+	};
+
+	static const uint8_t send_mo_mt_forward_sm_err[] = {
+		0x25, /* OSMO_GSUP_MSGT_MO_FORWARD_SM_ERROR */
+		TEST_IMSI_IE,
+
+		/* Session related IEs */
+		0x30, 0x04, /* Session ID */
+			0xde, 0xad, 0xbe, 0xef,
+		0x31, 0x01, /* Session state (END) */
+			0x03,
+
+		/* SM related IEs */
+		0x40, 0x01, /* SM-RP-MR (Message Reference) */
+			0xfa,
+		0x44, 0x01, /* SM-RP-Cause value */
+			0xaf,
+	};
+
+	static const uint8_t send_mo_mt_forward_sm_rsp[] = {
+		0x2a, /* OSMO_GSUP_MSGT_MT_FORWARD_SM_RESULT */
+		TEST_IMSI_IE,
+
+		/* SM related IEs */
+		0x40, 0x01, /* SM-RP-MR (Message Reference) */
+			0xfa,
+		0x43, 0x04, /* SM-RP-UI (TPDU) */
+			0xde, 0xad, 0xbe, 0xef,
+	};
+
 	static const struct test {
 		char *name;
 		const uint8_t *data;
@@ -256,6 +319,14 @@
 			send_ussd_req, sizeof(send_ussd_req)},
 		{"SS/USSD processUnstructuredSS-Request / ReturnResult",
 			send_ussd_res, sizeof(send_ussd_res)},
+		{"MO-ForwardSM (MSC -> SMSC) Request",
+			send_mo_forward_sm_req, sizeof(send_mo_forward_sm_req)},
+		{"MT-ForwardSM (MSC -> SMSC) Request",
+			send_mt_forward_sm_req, sizeof(send_mt_forward_sm_req)},
+		{"MO-/MT-ForwardSM Response",
+			send_mo_mt_forward_sm_rsp, sizeof(send_mo_mt_forward_sm_rsp)},
+		{"MO-/MT-ForwardSM Error",
+			send_mo_mt_forward_sm_err, sizeof(send_mo_mt_forward_sm_err)},
 	};
 
 	printf("Test GSUP message decoding/encoding\n");
@@ -323,7 +394,7 @@
 				 * FIXME: share the maximal IE value somehow
 				 * in order to avoid manual updating of this
 				 */
-				OSMO_ASSERT(t->data[j+0] <= OSMO_GSUP_SS_INFO_IE);
+				OSMO_ASSERT(t->data[j+0] <= OSMO_GSUP_SM_RP_MMS_IE);
 				OSMO_ASSERT(t->data[j+1] <= ie_end - j - 2);
 
 				ie_end = j;
diff --git a/tests/gsup/gsup_test.err b/tests/gsup/gsup_test.err
index ac71ac2..4a1357c 100644
--- a/tests/gsup/gsup_test.err
+++ b/tests/gsup/gsup_test.err
@@ -49,6 +49,18 @@
   generated message: 22 01 08 21 43 65 87 09 21 43 f5 30 04 de ad be ef 31 01 03 35 08 a3 06 02 01 01 02 01 47 
   original message:  22 01 08 21 43 65 87 09 21 43 f5 30 04 de ad be ef 31 01 03 35 08 a3 06 02 01 01 02 01 47 
   IMSI:              123456789012345
+  generated message: 24 01 08 21 43 65 87 09 21 43 f5 40 01 fa 41 08 03 91 52 75 47 99 09 82 42 01 ff 43 04 de ad be ef 
+  original message:  24 01 08 21 43 65 87 09 21 43 f5 40 01 fa 41 08 03 91 52 75 47 99 09 82 42 01 ff 43 04 de ad be ef 
+  IMSI:              123456789012345
+  generated message: 28 01 08 21 43 65 87 09 21 43 f5 40 01 fa 41 09 01 21 43 65 87 09 21 43 f5 42 08 03 91 52 75 47 99 09 82 43 04 de ad be ef 45 01 01 
+  original message:  28 01 08 21 43 65 87 09 21 43 f5 40 01 fa 41 09 01 21 43 65 87 09 21 43 f5 42 08 03 91 52 75 47 99 09 82 43 04 de ad be ef 45 01 01 
+  IMSI:              123456789012345
+  generated message: 2a 01 08 21 43 65 87 09 21 43 f5 40 01 fa 43 04 de ad be ef 
+  original message:  2a 01 08 21 43 65 87 09 21 43 f5 40 01 fa 43 04 de ad be ef 
+  IMSI:              123456789012345
+  generated message: 25 01 08 21 43 65 87 09 21 43 f5 30 04 de ad be ef 31 01 03 40 01 fa 44 01 af 
+  original message:  25 01 08 21 43 65 87 09 21 43 f5 30 04 de ad be ef 31 01 03 40 01 fa 44 01 af 
+  IMSI:              123456789012345
   message 0: tested 11 truncations, 11 parse failures
   message 1: tested 14 truncations, 13 parse failures
   message 2: tested 83 truncations, 81 parse failures
@@ -66,21 +78,29 @@
   message 14: tested 20 truncations, 18 parse failures
   message 15: tested 42 truncations, 39 parse failures
   message 16: tested 30 truncations, 27 parse failures
+  message 17: tested 33 truncations, 29 parse failures
+  message 18: tested 44 truncations, 39 parse failures
+  message 19: tested 20 truncations, 18 parse failures
+  message 20: tested 26 truncations, 22 parse failures
 DLGSUP Stopping DLGSUP logging
   message 0: tested 2816 modifications, 510 parse failures
-  message 1: tested 3584 modifications, 768 parse failures
-  message 2: tested 21248 modifications, 2571 parse failures
+  message 1: tested 3584 modifications, 770 parse failures
+  message 2: tested 21248 modifications, 2575 parse failures
   message 3: tested 2816 modifications, 510 parse failures
-  message 4: tested 3584 modifications, 768 parse failures
-  message 5: tested 20736 modifications, 4010 parse failures
-  message 6: tested 3584 modifications, 769 parse failures
-  message 7: tested 3584 modifications, 768 parse failures
+  message 4: tested 3584 modifications, 770 parse failures
+  message 5: tested 20736 modifications, 4022 parse failures
+  message 6: tested 3584 modifications, 771 parse failures
+  message 7: tested 3584 modifications, 770 parse failures
   message 8: tested 2816 modifications, 510 parse failures
   message 9: tested 2816 modifications, 510 parse failures
-  message 10: tested 3584 modifications, 768 parse failures
-  message 11: tested 3328 modifications, 767 parse failures
-  message 12: tested 54016 modifications, 4622 parse failures
+  message 10: tested 3584 modifications, 770 parse failures
+  message 11: tested 3328 modifications, 769 parse failures
+  message 12: tested 54016 modifications, 4626 parse failures
   message 13: tested 11520 modifications, 1026 parse failures
-  message 14: tested 5120 modifications, 1026 parse failures
-  message 15: tested 10752 modifications, 1256 parse failures
-  message 16: tested 7680 modifications, 1265 parse failures
+  message 14: tested 5120 modifications, 1030 parse failures
+  message 15: tested 10752 modifications, 1262 parse failures
+  message 16: tested 7680 modifications, 1271 parse failures
+  message 17: tested 8448 modifications, 2053 parse failures
+  message 18: tested 11264 modifications, 2307 parse failures
+  message 19: tested 5120 modifications, 1031 parse failures
+  message 20: tested 6656 modifications, 1546 parse failures
diff --git a/tests/gsup/gsup_test.ok b/tests/gsup/gsup_test.ok
index d63dd2d..7a9455d 100644
--- a/tests/gsup/gsup_test.ok
+++ b/tests/gsup/gsup_test.ok
@@ -33,4 +33,12 @@
           SS/USSD processUnstructuredSS-Request / Invoke OK
   Testing SS/USSD processUnstructuredSS-Request / ReturnResult
           SS/USSD processUnstructuredSS-Request / ReturnResult OK
+  Testing MO-ForwardSM (MSC -> SMSC) Request
+          MO-ForwardSM (MSC -> SMSC) Request OK
+  Testing MT-ForwardSM (MSC -> SMSC) Request
+          MT-ForwardSM (MSC -> SMSC) Request OK
+  Testing MO-/MT-ForwardSM Response
+          MO-/MT-ForwardSM Response OK
+  Testing MO-/MT-ForwardSM Error
+          MO-/MT-ForwardSM Error OK
 Done.