diff --git a/cpu/atmega_common/periph/spi.c b/cpu/atmega_common/periph/spi.c
index bdeceeba6e..a6af1f7d31 100644
--- a/cpu/atmega_common/periph/spi.c
+++ b/cpu/atmega_common/periph/spi.c
@@ -92,8 +92,8 @@ void spi_release(spi_t bus)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *out_buf = (uint8_t *)out;
-    uint8_t *in_buf = (uint8_t *)in;
+    const uint8_t *out_buf = out;
+    uint8_t *in_buf = in;
 
     assert(out_buf || in_buf);
 
diff --git a/cpu/cc2538/periph/spi.c b/cpu/cc2538/periph/spi.c
index 335fab1625..f4106acb77 100644
--- a/cpu/cc2538/periph/spi.c
+++ b/cpu/cc2538/periph/spi.c
@@ -126,8 +126,8 @@ void spi_release(spi_t bus)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *out_buf = (uint8_t *)out;
-    uint8_t *in_buf = (uint8_t *)in;
+    const uint8_t *out_buf = out;
+    uint8_t *in_buf = in;
 
     assert(out_buf || in_buf);
 
diff --git a/cpu/kinetis_common/periph/spi.c b/cpu/kinetis_common/periph/spi.c
index 5c5e157b38..095fa50419 100644
--- a/cpu/kinetis_common/periph/spi.c
+++ b/cpu/kinetis_common/periph/spi.c
@@ -161,8 +161,8 @@ void spi_release(spi_t bus)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *out_buf = (uint8_t *)out;
-    uint8_t *in_buf = (uint8_t *)in;
+    const uint8_t *out_buf = out;
+    uint8_t *in_buf = in;
     uint32_t flags = SPI_PUSHR_CONT_MASK;
 
     assert(out_buf || in_buf);
diff --git a/cpu/lpc11u34/periph/spi.c b/cpu/lpc11u34/periph/spi.c
index 61109d44e9..6e100221da 100644
--- a/cpu/lpc11u34/periph/spi.c
+++ b/cpu/lpc11u34/periph/spi.c
@@ -131,8 +131,8 @@ void spi_release(spi_t bus)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *out_buf = (uint8_t *)out;
-    uint8_t *in_buf = (uint8_t *)in;
+    const uint8_t *out_buf = out;
+    uint8_t *in_buf = in;
 
     assert(out_buf || in_buf);
 
diff --git a/cpu/lpc2387/periph/spi.c b/cpu/lpc2387/periph/spi.c
index 81901c6edf..abeff89769 100644
--- a/cpu/lpc2387/periph/spi.c
+++ b/cpu/lpc2387/periph/spi.c
@@ -107,8 +107,8 @@ void spi_release(spi_t bus)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *out_buf = (uint8_t *)out;
-    uint8_t *in_buf = (uint8_t *)in;
+    const uint8_t *out_buf = out;
+    uint8_t *in_buf = in;
 
     assert(out_buf || in_buf);
 
diff --git a/cpu/msp430fxyz/periph/spi.c b/cpu/msp430fxyz/periph/spi.c
index c178e0ed1b..50dd3aa7b8 100644
--- a/cpu/msp430fxyz/periph/spi.c
+++ b/cpu/msp430fxyz/periph/spi.c
@@ -115,8 +115,8 @@ void spi_release(spi_t dev)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *out_buf = (uint8_t *)out;
-    uint8_t *in_buf = (uint8_t *)in;
+    const uint8_t *out_buf = out;
+    uint8_t *in_buf = in;
 
     assert(out_buf || in_buf);
 
@@ -128,7 +128,7 @@ void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
     if (!in_buf) {
         for (size_t i = 0; i < len; i++) {
             while (!(SPI_IF & SPI_IE_TX_BIT)) {}
-            SPI_BASE->TXBUF = (uint8_t)out_buf[i];
+            SPI_BASE->TXBUF = out_buf[i];
         }
         /* finally we need to wait, until all transfers are complete */
 #ifndef SPI_USE_USCI
diff --git a/cpu/nrf5x_common/periph/spi.c b/cpu/nrf5x_common/periph/spi.c
index dec0538eb3..7e4fb3dfde 100644
--- a/cpu/nrf5x_common/periph/spi.c
+++ b/cpu/nrf5x_common/periph/spi.c
@@ -90,8 +90,8 @@ void spi_release(spi_t bus)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *in_buf = (uint8_t *)in;
-    uint8_t *out_buf = (uint8_t *)out;
+    const uint8_t *out_buf = out;
+    uint8_t *in_buf = in;
 
     assert(out_buf || in_buf);
 
diff --git a/cpu/sam0_common/periph/spi.c b/cpu/sam0_common/periph/spi.c
index e421310b42..7ddba30156 100644
--- a/cpu/sam0_common/periph/spi.c
+++ b/cpu/sam0_common/periph/spi.c
@@ -155,8 +155,8 @@ void spi_release(spi_t bus)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *out_buf = (uint8_t *)out;
-    uint8_t *in_buf = (uint8_t *)in;
+    const uint8_t *out_buf = out;
+    uint8_t *in_buf = in;
 
     assert(out || in);
 
diff --git a/cpu/sam3/periph/spi.c b/cpu/sam3/periph/spi.c
index cf2e0b62d6..967e7c5117 100644
--- a/cpu/sam3/periph/spi.c
+++ b/cpu/sam3/periph/spi.c
@@ -88,8 +88,8 @@ void spi_release(spi_t bus)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *out_buf = (uint8_t *)out;
-    uint8_t *in_buf = (uint8_t *)in;
+    const uint8_t *out_buf = out;
+    uint8_t *in_buf = in;
 
     assert(in_buf || out_buf);
 
diff --git a/cpu/stm32_common/periph/spi.c b/cpu/stm32_common/periph/spi.c
index cee13ca87f..65b08f7508 100644
--- a/cpu/stm32_common/periph/spi.c
+++ b/cpu/stm32_common/periph/spi.c
@@ -151,8 +151,8 @@ void spi_release(spi_t bus)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
-    uint8_t *inbuf = (uint8_t *)in;
-    uint8_t *outbuf = (uint8_t *)out;
+    const uint8_t *outbuf = out;
+    uint8_t *inbuf = in;
 
     /* make sure at least one input or one output buffer is given */
     assert(outbuf || inbuf);