diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index f8858865c5bb..5fc8540a83e3 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -244,16 +244,18 @@ enum gsm_encoding {
 
 enum gsm_mux_state {
 	GSM_SEARCH,
-	GSM_START,
-	GSM_ADDRESS,
-	GSM_CONTROL,
-	GSM_LEN,
-	GSM_DATA,
-	GSM_FCS,
-	GSM_OVERRUN,
-	GSM_LEN0,
-	GSM_LEN1,
-	GSM_SSOF,
+	GSM0_ADDRESS,
+	GSM0_CONTROL,
+	GSM0_LEN0,
+	GSM0_LEN1,
+	GSM0_DATA,
+	GSM0_FCS,
+	GSM0_SSOF,
+	GSM1_START,
+	GSM1_ADDRESS,
+	GSM1_CONTROL,
+	GSM1_DATA,
+	GSM1_OVERRUN,
 };
 
 /*
@@ -2846,6 +2848,30 @@ invalid:
 	return;
 }
 
+/**
+ * gsm0_receive_state_check_and_fix	-	check and correct receive state
+ * @gsm: gsm data for this ldisc instance
+ *
+ * Ensures that the current receive state is valid for basic option mode.
+ */
+
+static void gsm0_receive_state_check_and_fix(struct gsm_mux *gsm)
+{
+	switch (gsm->state) {
+	case GSM_SEARCH:
+	case GSM0_ADDRESS:
+	case GSM0_CONTROL:
+	case GSM0_LEN0:
+	case GSM0_LEN1:
+	case GSM0_DATA:
+	case GSM0_FCS:
+	case GSM0_SSOF:
+		break;
+	default:
+		gsm->state = GSM_SEARCH;
+		break;
+	}
+}
 
 /**
  *	gsm0_receive	-	perform processing for non-transparency
@@ -2859,26 +2885,27 @@ static void gsm0_receive(struct gsm_mux *gsm, unsigned char c)
 {
 	unsigned int len;
 
+	gsm0_receive_state_check_and_fix(gsm);
 	switch (gsm->state) {
 	case GSM_SEARCH:	/* SOF marker */
 		if (c == GSM0_SOF) {
-			gsm->state = GSM_ADDRESS;
+			gsm->state = GSM0_ADDRESS;
 			gsm->address = 0;
 			gsm->len = 0;
 			gsm->fcs = INIT_FCS;
 		}
 		break;
-	case GSM_ADDRESS:	/* Address EA */
+	case GSM0_ADDRESS:	/* Address EA */
 		gsm->fcs = gsm_fcs_add(gsm->fcs, c);
 		if (gsm_read_ea(&gsm->address, c))
-			gsm->state = GSM_CONTROL;
+			gsm->state = GSM0_CONTROL;
 		break;
-	case GSM_CONTROL:	/* Control Byte */
+	case GSM0_CONTROL:	/* Control Byte */
 		gsm->fcs = gsm_fcs_add(gsm->fcs, c);
 		gsm->control = c;
-		gsm->state = GSM_LEN0;
+		gsm->state = GSM0_LEN0;
 		break;
-	case GSM_LEN0:		/* Length EA */
+	case GSM0_LEN0:		/* Length EA */
 		gsm->fcs = gsm_fcs_add(gsm->fcs, c);
 		if (gsm_read_ea(&gsm->len, c)) {
 			if (gsm->len > gsm->mru) {
@@ -2888,14 +2915,14 @@ static void gsm0_receive(struct gsm_mux *gsm, unsigned char c)
 			}
 			gsm->count = 0;
 			if (!gsm->len)
-				gsm->state = GSM_FCS;
+				gsm->state = GSM0_FCS;
 			else
-				gsm->state = GSM_DATA;
+				gsm->state = GSM0_DATA;
 			break;
 		}
-		gsm->state = GSM_LEN1;
+		gsm->state = GSM0_LEN1;
 		break;
-	case GSM_LEN1:
+	case GSM0_LEN1:
 		gsm->fcs = gsm_fcs_add(gsm->fcs, c);
 		len = c;
 		gsm->len |= len << 7;
@@ -2906,11 +2933,11 @@ static void gsm0_receive(struct gsm_mux *gsm, unsigned char c)
 		}
 		gsm->count = 0;
 		if (!gsm->len)
-			gsm->state = GSM_FCS;
+			gsm->state = GSM0_FCS;
 		else
-			gsm->state = GSM_DATA;
+			gsm->state = GSM0_DATA;
 		break;
-	case GSM_DATA:		/* Data */
+	case GSM0_DATA:		/* Data */
 		gsm->buf[gsm->count++] = c;
 		if (gsm->count >= MAX_MRU) {
 			gsm->bad_size++;
@@ -2921,14 +2948,14 @@ static void gsm0_receive(struct gsm_mux *gsm, unsigned char c)
 				gsm->fcs = gsm_fcs_add_block(gsm->fcs, gsm->buf,
 							     gsm->count);
 			}
-			gsm->state = GSM_FCS;
+			gsm->state = GSM0_FCS;
 		}
 		break;
-	case GSM_FCS:		/* FCS follows the packet */
+	case GSM0_FCS:		/* FCS follows the packet */
 		gsm->fcs = gsm_fcs_add(gsm->fcs, c);
-		gsm->state = GSM_SSOF;
+		gsm->state = GSM0_SSOF;
 		break;
-	case GSM_SSOF:
+	case GSM0_SSOF:
 		gsm->state = GSM_SEARCH;
 		if (c == GSM0_SOF)
 			gsm_queue(gsm);
@@ -2941,6 +2968,29 @@ static void gsm0_receive(struct gsm_mux *gsm, unsigned char c)
 	}
 }
 
+/**
+ * gsm1_receive_state_check_and_fix	-	check and correct receive state
+ * @gsm: gsm data for this ldisc instance
+ *
+ * Ensures that the current receive state is valid for advanced option mode.
+ */
+
+static void gsm1_receive_state_check_and_fix(struct gsm_mux *gsm)
+{
+	switch (gsm->state) {
+	case GSM_SEARCH:
+	case GSM1_START:
+	case GSM1_ADDRESS:
+	case GSM1_CONTROL:
+	case GSM1_DATA:
+	case GSM1_OVERRUN:
+		break;
+	default:
+		gsm->state = GSM_SEARCH;
+		break;
+	}
+}
+
 /**
  *	gsm1_receive	-	perform processing for non-transparency
  *	@gsm: gsm data for this ldisc instance
@@ -2951,6 +3001,7 @@ static void gsm0_receive(struct gsm_mux *gsm, unsigned char c)
 
 static void gsm1_receive(struct gsm_mux *gsm, unsigned char c)
 {
+	gsm1_receive_state_check_and_fix(gsm);
 	/* handle XON/XOFF */
 	if ((c & ISO_IEC_646_MASK) == XON) {
 		gsm->constipated = true;
@@ -2963,11 +3014,11 @@ static void gsm1_receive(struct gsm_mux *gsm, unsigned char c)
 	}
 	if (c == GSM1_SOF) {
 		/* EOF is only valid in frame if we have got to the data state */
-		if (gsm->state == GSM_DATA) {
+		if (gsm->state == GSM1_DATA) {
 			if (gsm->count < 1) {
 				/* Missing FSC */
 				gsm->malformed++;
-				gsm->state = GSM_START;
+				gsm->state = GSM1_START;
 				return;
 			}
 			/* Remove the FCS from data */
@@ -2983,14 +3034,14 @@ static void gsm1_receive(struct gsm_mux *gsm, unsigned char c)
 			gsm->fcs = gsm_fcs_add(gsm->fcs, gsm->buf[gsm->count]);
 			gsm->len = gsm->count;
 			gsm_queue(gsm);
-			gsm->state  = GSM_START;
+			gsm->state  = GSM1_START;
 			return;
 		}
 		/* Any partial frame was a runt so go back to start */
-		if (gsm->state != GSM_START) {
+		if (gsm->state != GSM1_START) {
 			if (gsm->state != GSM_SEARCH)
 				gsm->malformed++;
-			gsm->state = GSM_START;
+			gsm->state = GSM1_START;
 		}
 		/* A SOF in GSM_START means we are still reading idling or
 		   framing bytes */
@@ -3011,30 +3062,30 @@ static void gsm1_receive(struct gsm_mux *gsm, unsigned char c)
 		gsm->escape = false;
 	}
 	switch (gsm->state) {
-	case GSM_START:		/* First byte after SOF */
+	case GSM1_START:		/* First byte after SOF */
 		gsm->address = 0;
-		gsm->state = GSM_ADDRESS;
+		gsm->state = GSM1_ADDRESS;
 		gsm->fcs = INIT_FCS;
 		fallthrough;
-	case GSM_ADDRESS:	/* Address continuation */
+	case GSM1_ADDRESS:	/* Address continuation */
 		gsm->fcs = gsm_fcs_add(gsm->fcs, c);
 		if (gsm_read_ea(&gsm->address, c))
-			gsm->state = GSM_CONTROL;
+			gsm->state = GSM1_CONTROL;
 		break;
-	case GSM_CONTROL:	/* Control Byte */
+	case GSM1_CONTROL:	/* Control Byte */
 		gsm->fcs = gsm_fcs_add(gsm->fcs, c);
 		gsm->control = c;
 		gsm->count = 0;
-		gsm->state = GSM_DATA;
+		gsm->state = GSM1_DATA;
 		break;
-	case GSM_DATA:		/* Data */
+	case GSM1_DATA:		/* Data */
 		if (gsm->count > gsm->mru || gsm->count > MAX_MRU) {	/* Allow one for the FCS */
-			gsm->state = GSM_OVERRUN;
+			gsm->state = GSM1_OVERRUN;
 			gsm->bad_size++;
 		} else
 			gsm->buf[gsm->count++] = c;
 		break;
-	case GSM_OVERRUN:	/* Over-long - eg a dropped SOF */
+	case GSM1_OVERRUN:	/* Over-long - eg a dropped SOF */
 		break;
 	default:
 		pr_debug("%s: unhandled state: %d\n", __func__, gsm->state);