diff --git a/src/libosmo-mgcp/mgcp_msg.c b/src/libosmo-mgcp/mgcp_msg.c
index f732158..648d86b 100644
--- a/src/libosmo-mgcp/mgcp_msg.c
+++ b/src/libosmo-mgcp/mgcp_msg.c
@@ -454,10 +454,10 @@
 	}
 
 	/* Check for over long connection identifiers */
-	if (strlen(conn_id) > MGCP_CONN_ID_MAXLEN) {
+	if (strlen(conn_id) > (MGCP_CONN_ID_MAXLEN-1)) {
 		LOGP(DLMGCP, LOGL_ERROR,
-		     "endpoint:0x%x invalid ConnectionIdentifier (too long) 0x%s\n",
-		     ENDPOINT_NUMBER(endp), conn_id);
+		     "endpoint:0x%x invalid ConnectionIdentifier (too long: %zu > %d) 0x%s\n",
+		     ENDPOINT_NUMBER(endp), strlen(conn_id), MGCP_CONN_ID_MAXLEN-1, conn_id);
 		return 510;
 	}
 
diff --git a/tests/mgcp/mgcp_test.c b/tests/mgcp/mgcp_test.c
index 2f3a8a7..c40eabc 100644
--- a/tests/mgcp/mgcp_test.c
+++ b/tests/mgcp/mgcp_test.c
@@ -230,6 +230,12 @@
 	"I: %s\r\n" \
 	"L: p:20, a:AMR, nt:IN\r\n"
 
+#define MDCX_TOO_LONG_CI \
+	"MDCX 18983222 1@mgw MGCP 1.0\r\n" \
+	"I: 123456789012345678901234567890123\n"
+
+#define MDCX_TOO_LONG_CI_RET "510 18983222 FAIL\r\n"
+
 #define SHORT2	"CRCX 1"
 #define SHORT2_RET "510 000000 FAIL\r\n"
 #define SHORT3	"CRCX 1 1@mgw"
@@ -510,6 +516,7 @@
 	{"DLCX", DLCX, DLCX_RET, PTYPE_IGNORE,.extra_fmtp = "a=fmtp:126 0/1/2"},
 	{"CRCX", CRCX_NO_LCO_NO_SDP, CRCX_NO_LCO_NO_SDP_RET, 97},
 	{"CRCX", CRCX_X_OSMO_IGN, CRCX_X_OSMO_IGN_RET, 97},
+	{"MDCX_TOO_LONG_CI", MDCX_TOO_LONG_CI, MDCX_TOO_LONG_CI_RET},
 };
 
 static const struct mgcp_test retransmit[] = {
diff --git a/tests/mgcp/mgcp_test.ok b/tests/mgcp/mgcp_test.ok
index 915d45e..ddda751 100644
--- a/tests/mgcp/mgcp_test.ok
+++ b/tests/mgcp/mgcp_test.ok
Binary files differ