diff --git a/drivers/modem/gsm_ppp.c b/drivers/modem/gsm_ppp.c
index 85f0e7029c2..1b4bec1e801 100644
--- a/drivers/modem/gsm_ppp.c
+++ b/drivers/modem/gsm_ppp.c
@@ -50,7 +50,6 @@ static struct gsm_modem {
 
 	struct modem_iface_uart_data gsm_data;
 	struct k_delayed_work gsm_configure_work;
-	char gsm_isr_buf[PPP_MRU];
 	char gsm_rx_rb_buf[PPP_MRU * 3];
 
 	uint8_t *ppp_recv_buf;
@@ -647,8 +646,6 @@ static int gsm_init(const struct device *device)
 #endif	/* CONFIG_MODEM_SIM_NUMBERS */
 #endif	/* CONFIG_MODEM_SHELL */
 
-	gsm->gsm_data.isr_buf = &gsm->gsm_isr_buf[0];
-	gsm->gsm_data.isr_buf_len = sizeof(gsm->gsm_isr_buf);
 	gsm->gsm_data.rx_rb_buf = &gsm->gsm_rx_rb_buf[0];
 	gsm->gsm_data.rx_rb_buf_len = sizeof(gsm->gsm_rx_rb_buf);
 
diff --git a/drivers/modem/modem_iface_uart.c b/drivers/modem/modem_iface_uart.c
index 89ef8d346ee..0bed06e56f2 100644
--- a/drivers/modem/modem_iface_uart.c
+++ b/drivers/modem/modem_iface_uart.c
@@ -53,6 +53,9 @@ static void modem_iface_uart_isr(const struct device *uart_dev,
 	struct modem_context *ctx;
 	struct modem_iface_uart_data *data;
 	int rx = 0, ret;
+	uint8_t *dst;
+	uint32_t partial_size = 0;
+	uint32_t total_size = 0;
 
 	ARG_UNUSED(user_data);
 
@@ -66,22 +69,30 @@ static void modem_iface_uart_isr(const struct device *uart_dev,
 	/* get all of the data off UART as fast as we can */
 	while (uart_irq_update(ctx->iface.dev) &&
 	       uart_irq_rx_ready(ctx->iface.dev)) {
-		rx = uart_fifo_read(ctx->iface.dev,
-				    data->isr_buf, data->isr_buf_len);
+		if (!partial_size) {
+			partial_size = ring_buf_put_claim(&data->rx_rb, &dst,
+							  UINT32_MAX);
+		}
+		if (!partial_size) {
+			LOG_ERR("Rx buffer doesn't have enough space");
+			modem_iface_uart_flush(&ctx->iface);
+			break;
+		}
+
+		rx = uart_fifo_read(ctx->iface.dev, dst, partial_size);
 		if (rx <= 0) {
 			continue;
 		}
 
-		ret = ring_buf_put(&data->rx_rb, data->isr_buf, rx);
-		if (ret != rx) {
-			LOG_ERR("Rx buffer doesn't have enough space. "
-				"Bytes pending: %d, written: %d",
-				rx, ret);
-			modem_iface_uart_flush(&ctx->iface);
-			k_sem_give(&data->rx_sem);
-			break;
-		}
+		dst += rx;
+		total_size += rx;
+		partial_size -= rx;
+	}
 
+	ret = ring_buf_put_finish(&data->rx_rb, total_size);
+	__ASSERT_NO_MSG(ret == 0);
+
+	if (total_size > 0) {
 		k_sem_give(&data->rx_sem);
 	}
 }
diff --git a/drivers/modem/modem_iface_uart.h b/drivers/modem/modem_iface_uart.h
index d0b918ab016..98ef8665fbb 100644
--- a/drivers/modem/modem_iface_uart.h
+++ b/drivers/modem/modem_iface_uart.h
@@ -20,10 +20,6 @@ extern "C" {
 #endif
 
 struct modem_iface_uart_data {
-	/* ISR char buffer */
-	char *isr_buf;
-	size_t isr_buf_len;
-
 	/* ring buffer char buffer */
 	char *rx_rb_buf;
 	size_t rx_rb_buf_len;
diff --git a/drivers/modem/ublox-sara-r4.c b/drivers/modem/ublox-sara-r4.c
index 2e0620d4e16..9abf2035a42 100644
--- a/drivers/modem/ublox-sara-r4.c
+++ b/drivers/modem/ublox-sara-r4.c
@@ -131,7 +131,6 @@ struct modem_data {
 
 	/* modem interface */
 	struct modem_iface_uart_data iface_data;
-	uint8_t iface_isr_buf[MDM_RECV_BUF_SIZE];
 	uint8_t iface_rb_buf[MDM_MAX_DATA_LENGTH];
 
 	/* modem cmds */
@@ -1755,8 +1754,6 @@ static int modem_init(const struct device *dev)
 	}
 
 	/* modem interface */
-	mdata.iface_data.isr_buf = &mdata.iface_isr_buf[0];
-	mdata.iface_data.isr_buf_len = sizeof(mdata.iface_isr_buf);
 	mdata.iface_data.rx_rb_buf = &mdata.iface_rb_buf[0];
 	mdata.iface_data.rx_rb_buf_len = sizeof(mdata.iface_rb_buf);
 	ret = modem_iface_uart_init(&mctx.iface, &mdata.iface_data,
diff --git a/drivers/wifi/esp/esp.c b/drivers/wifi/esp/esp.c
index 0cbe3078882..373bfdc7f68 100644
--- a/drivers/wifi/esp/esp.c
+++ b/drivers/wifi/esp/esp.c
@@ -880,8 +880,6 @@ static int esp_init(const struct device *dev)
 	}
 
 	/* modem interface */
-	data->iface_data.isr_buf = &data->iface_isr_buf[0];
-	data->iface_data.isr_buf_len = sizeof(data->iface_isr_buf);
 	data->iface_data.rx_rb_buf = &data->iface_rb_buf[0];
 	data->iface_data.rx_rb_buf_len = sizeof(data->iface_rb_buf);
 	ret = modem_iface_uart_init(&data->mctx.iface, &data->iface_data,
diff --git a/drivers/wifi/esp/esp.h b/drivers/wifi/esp/esp.h
index edff3381abf..4669aeec852 100644
--- a/drivers/wifi/esp/esp.h
+++ b/drivers/wifi/esp/esp.h
@@ -169,7 +169,6 @@ struct esp_data {
 
 	/* modem interface */
 	struct modem_iface_uart_data iface_data;
-	uint8_t iface_isr_buf[MDM_RECV_BUF_SIZE];
 	uint8_t iface_rb_buf[MDM_RING_BUF_SIZE];
 
 	/* modem cmds */