diff --git a/esp8266/modpybhspi.c b/esp8266/modpybhspi.c
index c1cd7f662d1710eb1b11462c8f8617ebc98a8213..10a090269f50060af1b90313fbcf197c7ce57060 100644
--- a/esp8266/modpybhspi.c
+++ b/esp8266/modpybhspi.c
@@ -50,23 +50,23 @@ typedef struct _pyb_hspi_obj_t {
 } pyb_hspi_obj_t;
 
 
-STATIC void hspi_transfer(mp_obj_base_t *self_in, size_t src_len, const uint8_t *src_buf, size_t dest_len, uint8_t *dest_buf) {
+STATIC void hspi_transfer(mp_obj_base_t *self_in, size_t len, const uint8_t *src, uint8_t *dest) {
     (void)self_in;
 
-    if (dest_len == 0) {
+    if (dest == NULL) {
         // fast case when we only need to write data
         size_t chunk_size = 1024;
-        size_t count = src_len / chunk_size;
+        size_t count = len / chunk_size;
         size_t i = 0;
         for (size_t j = 0; j < count; ++j) {
             for (size_t k = 0; k < chunk_size; ++k) {
-                spi_tx8fast(HSPI, src_buf[i]);
+                spi_tx8fast(HSPI, src[i]);
                 ++i;
             }
             ets_loop_iter();
         }
-        while (i < src_len) {
-            spi_tx8fast(HSPI, src_buf[i]);
+        while (i < len) {
+            spi_tx8fast(HSPI, src[i]);
             ++i;
         }
     } else {
@@ -74,29 +74,17 @@ STATIC void hspi_transfer(mp_obj_base_t *self_in, size_t src_len, const uint8_t
 
         // Process data in chunks, let the pending tasks run in between
         size_t chunk_size = 1024; // TODO this should depend on baudrate
-        size_t count = dest_len / chunk_size;
+        size_t count = len / chunk_size;
         size_t i = 0;
         for (size_t j = 0; j < count; ++j) {
             for (size_t k = 0; k < chunk_size; ++k) {
-                uint32_t data_out;
-                if (src_len == 1) {
-                    data_out = src_buf[0];
-                } else {
-                    data_out = src_buf[i];
-                }
-                dest_buf[i] = spi_transaction(HSPI, 0, 0, 0, 0, 8, data_out, 8, 0);
+                dest[i] = spi_transaction(HSPI, 0, 0, 0, 0, 8, src[i], 8, 0);
                 ++i;
             }
             ets_loop_iter();
         }
-        while (i < dest_len) {
-            uint32_t data_out;
-            if (src_len == 1) {
-                data_out = src_buf[0];
-            } else {
-                data_out = src_buf[i];
-            }
-            dest_buf[i] = spi_transaction(HSPI, 0, 0, 0, 0, 8, data_out, 8, 0);
+        while (i < len) {
+            dest[i] = spi_transaction(HSPI, 0, 0, 0, 0, 8, src[i], 8, 0);
             ++i;
         }
     }
diff --git a/esp8266/modpybspi.c b/esp8266/modpybspi.c
index 4c4b843c5d47ff4000085adab35fd9d229009ec3..b9650954f33e1be2470a4f741eb3f730ae5cb186 100644
--- a/esp8266/modpybspi.c
+++ b/esp8266/modpybspi.c
@@ -47,17 +47,12 @@ typedef struct _pyb_spi_obj_t {
     mp_hal_pin_obj_t miso;
 } pyb_spi_obj_t;
 
-STATIC void mp_hal_spi_transfer(mp_obj_base_t *self_in, size_t src_len, const uint8_t *src_buf, size_t dest_len, uint8_t *dest_buf) {
+STATIC void mp_hal_spi_transfer(mp_obj_base_t *self_in, size_t len, const uint8_t *src, uint8_t *dest) {
     pyb_spi_obj_t *self = (pyb_spi_obj_t*)self_in;
     // only MSB transfer is implemented
     uint32_t delay_half = 500000 / self->baudrate + 1;
-    for (size_t i = 0; i < src_len || i < dest_len; ++i) {
-        uint8_t data_out;
-        if (src_len == 1) {
-            data_out = src_buf[0];
-        } else {
-            data_out = src_buf[i];
-        }
+    for (size_t i = 0; i < len; ++i) {
+        uint8_t data_out = src[i];
         uint8_t data_in = 0;
         for (int j = 0; j < 8; ++j, data_out <<= 1) {
             mp_hal_pin_write(self->mosi, (data_out >> 7) & 1);
@@ -77,8 +72,8 @@ STATIC void mp_hal_spi_transfer(mp_obj_base_t *self_in, size_t src_len, const ui
                 ets_delay_us(delay_half);
             }
         }
-        if (dest_len != 0) {
-            dest_buf[i] = data_in;
+        if (dest != NULL) {
+            dest[i] = data_in;
         }
         // make sure pending tasks have a chance to run
         ets_loop_iter();
diff --git a/extmod/machine_spi.c b/extmod/machine_spi.c
index 6b6202a221e2193400534ef31cab1177f2f04a8d..1c64cf511b0dcc6f2ef5f304175760107915c662 100644
--- a/extmod/machine_spi.c
+++ b/extmod/machine_spi.c
@@ -25,26 +25,24 @@
  */
 
 #include <stdio.h>
+#include <string.h>
 
 #include "py/runtime.h"
 #include "extmod/machine_spi.h"
 
 #if MICROPY_PY_MACHINE_SPI
 
-STATIC void mp_machine_spi_transfer(mp_obj_t self, size_t slen, const uint8_t *src, size_t dlen, uint8_t *dest) {
+STATIC void mp_machine_spi_transfer(mp_obj_t self, size_t len, const void *src, void *dest) {
     mp_obj_base_t *s = (mp_obj_base_t*)MP_OBJ_TO_PTR(self);
     mp_machine_spi_p_t *spi_p = (mp_machine_spi_p_t*)s->type->protocol;
-    spi_p->transfer(s, slen, src, dlen, dest);
+    spi_p->transfer(s, len, src, dest);
 }
 
 STATIC mp_obj_t mp_machine_spi_read(size_t n_args, const mp_obj_t *args) {
-    uint8_t write_byte = 0;
-    if (n_args == 3) {
-        write_byte = mp_obj_get_int(args[2]);
-    }
     vstr_t vstr;
     vstr_init_len(&vstr, mp_obj_get_int(args[1]));
-    mp_machine_spi_transfer(args[0], 1, &write_byte, vstr.len, (uint8_t*)vstr.buf);
+    memset(vstr.buf, n_args == 3 ? mp_obj_get_int(args[2]) : 0, vstr.len);
+    mp_machine_spi_transfer(args[0], vstr.len, vstr.buf, vstr.buf);
     return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_machine_spi_read_obj, 2, 3, mp_machine_spi_read);
@@ -52,11 +50,8 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_machine_spi_read_obj, 2, 3, mp_machine_sp
 STATIC mp_obj_t mp_machine_spi_readinto(size_t n_args, const mp_obj_t *args) {
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[1], &bufinfo, MP_BUFFER_WRITE);
-    uint8_t write_byte = 0;
-    if (n_args == 3) {
-        write_byte = mp_obj_get_int(args[2]);
-    }
-    mp_machine_spi_transfer(args[0], 1, &write_byte, bufinfo.len, (uint8_t*)bufinfo.buf);
+    memset(bufinfo.buf, n_args == 3 ? mp_obj_get_int(args[2]) : 0, bufinfo.len);
+    mp_machine_spi_transfer(args[0], bufinfo.len, bufinfo.buf, bufinfo.buf);
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_machine_spi_readinto_obj, 2, 3, mp_machine_spi_readinto);
@@ -64,7 +59,7 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_machine_spi_readinto_obj, 2, 3, mp_machin
 STATIC mp_obj_t mp_machine_spi_write(mp_obj_t self, mp_obj_t wr_buf) {
     mp_buffer_info_t src;
     mp_get_buffer_raise(wr_buf, &src, MP_BUFFER_READ);
-    mp_machine_spi_transfer(self, src.len, (const uint8_t*)src.buf, 0, NULL);
+    mp_machine_spi_transfer(self, src.len, (const uint8_t*)src.buf, NULL);
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_2(mp_machine_spi_write_obj, mp_machine_spi_write);
@@ -75,9 +70,9 @@ STATIC mp_obj_t mp_machine_spi_write_readinto(mp_obj_t self, mp_obj_t wr_buf, mp
     mp_buffer_info_t dest;
     mp_get_buffer_raise(rd_buf, &dest, MP_BUFFER_WRITE);
     if (src.len != dest.len) {
-        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "buffers must be the same length"));
+        mp_raise_ValueError("buffers must be the same length");
     }
-    mp_machine_spi_transfer(self, src.len, (const uint8_t*)src.buf, dest.len, (uint8_t*)dest.buf);
+    mp_machine_spi_transfer(self, src.len, src.buf, dest.buf);
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_3(mp_machine_spi_write_readinto_obj, mp_machine_spi_write_readinto);
diff --git a/extmod/machine_spi.h b/extmod/machine_spi.h
index 26d716fc1141d5014325fe201b729f9782ca7bd7..35a911d91931513883ce54ed0e20f902c87bbd23 100644
--- a/extmod/machine_spi.h
+++ b/extmod/machine_spi.h
@@ -31,7 +31,7 @@
 
 // SPI protocol
 typedef struct _mp_machine_spi_p_t {
-    void (*transfer)(mp_obj_base_t *obj, size_t slen, const uint8_t *src, size_t dlen, uint8_t *dest);
+    void (*transfer)(mp_obj_base_t *obj, size_t len, const uint8_t *src, uint8_t *dest);
 } mp_machine_spi_p_t;
 
 MP_DECLARE_CONST_FUN_OBJ(mp_machine_spi_read_obj);
diff --git a/stmhal/spi.c b/stmhal/spi.c
index 85f1709200424361681a86df694588b0695da0d5..05b9b629c534ebf58e633dd32172e7a5229670b9 100644
--- a/stmhal/spi.c
+++ b/stmhal/spi.c
@@ -401,15 +401,8 @@ STATIC void spi_transfer(mp_obj_base_t *self_in, size_t src_len, const uint8_t *
     }
 }
 
-STATIC void spi_transfer_machine(mp_obj_base_t *self_in, size_t src_len, const uint8_t *src_buf, size_t dest_len, uint8_t *dest_buf) {
-    if (src_len == 1 && dest_len > 1) {
-        // this catches read and readinto
-        // copy the single output byte to the dest buffer and use that as source
-        memset(dest_buf, src_buf[0], dest_len);
-        src_len = dest_len;
-        src_buf = dest_buf;
-    }
-    spi_transfer(self_in, src_len, src_buf, dest_len, dest_buf, 100);
+STATIC void spi_transfer_machine(mp_obj_base_t *self_in, size_t len, const uint8_t *src, uint8_t *dest) {
+    spi_transfer(self_in, len, src, dest == NULL ? 0 : len, dest, 100);
 }
 
 /******************************************************************************/