diff --git a/subsys/modem/modem_cmux.c b/subsys/modem/modem_cmux.c
index 690af4ddce8..a73241a7a46 100644
--- a/subsys/modem/modem_cmux.c
+++ b/subsys/modem/modem_cmux.c
@@ -23,7 +23,7 @@ LOG_MODULE_REGISTER(modem_cmux, CONFIG_MODEM_MODULES_LOG_LEVEL);
 #define MODEM_CMUX_DATA_FRAME_SIZE_MIN		(MODEM_CMUX_FRAME_SIZE_MAX + \
 						 MODEM_CMUX_DATA_SIZE_MIN)
 
-#define MODEM_CMUX_CMD_DATA_SIZE_MAX		(0x04)
+#define MODEM_CMUX_CMD_DATA_SIZE_MAX		(0x08)
 #define MODEM_CMUX_CMD_FRAME_SIZE_MAX		(MODEM_CMUX_FRAME_SIZE_MAX + \
 						 MODEM_CMUX_CMD_DATA_SIZE_MAX)
 
diff --git a/tests/subsys/modem/modem_cmux/src/main.c b/tests/subsys/modem/modem_cmux/src/main.c
index 243aa6112c8..9df6837efc5 100644
--- a/tests/subsys/modem/modem_cmux/src/main.c
+++ b/tests/subsys/modem/modem_cmux/src/main.c
@@ -100,11 +100,11 @@ static uint8_t cmux_frame_dlci2_sabm_cmd[] = {0xF9, 0x0B, 0x3F, 0x01, 0x59, 0xF9
 static uint8_t cmux_frame_dlci2_sabm_ack[] = {0xF9, 0x0B, 0x73, 0x01, 0x92, 0xF9};
 static uint8_t cmux_frame_dlci2_disc_cmd[] = {0xF9, 0x0B, 0x53, 0x01, 0xB8, 0xF9};
 static uint8_t cmux_frame_dlci2_ua_ack[] = {0xF9, 0x0B, 0x73, 0x01, 0x92, 0xF9};
-static uint8_t cmux_frame_control_msc_cmd[] = {0xF9, 0x01, 0xFF, 0x09, 0xE3,
-					       0x05, 0x0B, 0x09, 0x8F, 0xF9};
+static uint8_t cmux_frame_control_msc_cmd[] = {0xF9, 0x01, 0xFF, 0x0B, 0xE3,
+					       0x07, 0x0B, 0x09, 0x01, 0x6C, 0xF9};
 
-static uint8_t cmux_frame_control_msc_ack[] = {0xF9, 0x01, 0xFF, 0x09, 0xE1,
-					       0x05, 0x0B, 0x09, 0x8F, 0xF9};
+static uint8_t cmux_frame_control_msc_ack[] = {0xF9, 0x01, 0xFF, 0x0B, 0xE1,
+					       0x07, 0x0B, 0x09, 0x01, 0x6C, 0xF9};
 
 static uint8_t cmux_frame_control_fcon_cmd[] = {0xF9, 0x01, 0xFF, 0x05, 0xA3, 0x01, 0x86, 0xF9};
 static uint8_t cmux_frame_control_fcon_ack[] = {0xF9, 0x01, 0xFF, 0x05, 0xA1, 0x01, 0x86, 0xF9};