diff --git a/cpu/atmega_common/periph/spi.c b/cpu/atmega_common/periph/spi.c
index bbb023015c..cac04cfdeb 100644
--- a/cpu/atmega_common/periph/spi.c
+++ b/cpu/atmega_common/periph/spi.c
@@ -24,10 +24,10 @@
  *
  * @}
  */
+#include <assert.h>
 
 #include "cpu.h"
 #include "mutex.h"
-#include "assert.h"
 #include "periph/spi.h"
 
 /**
@@ -78,10 +78,11 @@ void spi_init_pins(spi_t bus)
 #endif
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     (void)bus;
     (void)cs;
+    assert(bus == SPI_DEV(0));
 
     /* lock the bus and power on the SPI peripheral */
     mutex_lock(&lock);
@@ -94,8 +95,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
     /* clear interrupt flag by reading SPSR and data register by reading SPDR */
     (void)SPSR;
     (void)SPDR;
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/atxmega/periph/spi.c b/cpu/atxmega/periph/spi.c
index cc0d57dfc7..690bf73717 100644
--- a/cpu/atxmega/periph/spi.c
+++ b/cpu/atxmega/periph/spi.c
@@ -87,7 +87,7 @@ void spi_init_pins(spi_t bus)
     gpio_init(spi_config[bus].mosi_pin, GPIO_OUT);
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     (void)cs;
     (void)clk;
@@ -106,8 +106,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 
     (void)dev(bus)->STATUS;
     (void)dev(bus)->DATA;
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/cc2538/periph/spi.c b/cpu/cc2538/periph/spi.c
index ae258a9353..6798f43ae0 100644
--- a/cpu/cc2538/periph/spi.c
+++ b/cpu/cc2538/periph/spi.c
@@ -21,12 +21,13 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "vendor/hw_memmap.h"
 #include "vendor/hw_ssi.h"
 
 #include "cpu.h"
 #include "mutex.h"
-#include "assert.h"
 #include "periph/spi.h"
 
 #define ENABLE_DEBUG 0
@@ -93,10 +94,10 @@ void spi_init_pins(spi_t bus)
     gpio_init_mux(spi_config[bus].miso_pin, OVERRIDE_DISABLE, GPIO_MUX_NONE, rxd);
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     DEBUG("%s: bus=%u\n", __FUNCTION__, bus);
-    (void) cs;
+    (void)cs;
     /* lock the bus */
     mutex_lock(&locks[bus]);
     /* power on device */
@@ -107,8 +108,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
     dev(bus)->CR0 = ((spi_clk_config[clk].scr << 8) | mode | SSI_CR0_DSS(8));
     /* enable SSI device */
     dev(bus)->CR1 = SSI_CR1_SSE;
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
@@ -132,6 +131,7 @@ static uint8_t _trx(cc2538_ssi_t *dev, uint8_t in)
 void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
                         const void *out, void *in, size_t len)
 {
+    assert((unsigned)bus < SPI_NUMOF);
     DEBUG("%s: bus=%u, len=%u\n", __FUNCTION__, bus, (unsigned)len);
 
     const uint8_t *out_buf = out;
diff --git a/cpu/efm32/periph/spi.c b/cpu/efm32/periph/spi.c
index 2b7ab3e7f5..86c2afa90c 100644
--- a/cpu/efm32/periph/spi.c
+++ b/cpu/efm32/periph/spi.c
@@ -56,9 +56,10 @@ void spi_init_pins(spi_t bus)
     gpio_init(spi_config[bus].miso_pin, GPIO_IN_PD);
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     (void)cs;
+    assert((unsigned)bus < SPI_NUMOF);
 
     mutex_lock(&spi_lock[bus]);
 
@@ -68,8 +69,8 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 
     USART_InitSync_TypeDef init = USART_INITSYNC_DEFAULT;
 
-    init.baudrate = (uint32_t) clk;
-    init.clockMode = (USART_ClockMode_TypeDef) mode;
+    init.baudrate = (uint32_t)clk;
+    init.clockMode = (USART_ClockMode_TypeDef)mode;
     init.msbf = true;
 
     USART_InitSync(spi_config[bus].dev, &init);
@@ -86,8 +87,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
                                      USART_ROUTEPEN_TXPEN |
                                      USART_ROUTEPEN_CLKPEN);
 #endif
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/esp_common/periph/spi.c b/cpu/esp_common/periph/spi.c
index 388f5d3d08..20ddf85f20 100644
--- a/cpu/esp_common/periph/spi.c
+++ b/cpu/esp_common/periph/spi.c
@@ -289,7 +289,7 @@ int spi_init_cs(spi_t bus, spi_cs_t cs)
     return SPI_OK;
 }
 
-int IRAM_ATTR spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void IRAM_ATTR spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     DEBUG("%s bus=%u cs=%u mode=%u clk=%u\n", __func__, bus, cs, mode, clk);
 
@@ -308,7 +308,7 @@ int IRAM_ATTR spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk
         LOG_TAG_ERROR("spi",
                       "SPI_DEV(%d) CS signal could not be initialized\n",
                       bus);
-        return SPI_NOCS;
+        assert(0);
     }
 
     /* lock the bus */
@@ -375,8 +375,6 @@ int IRAM_ATTR spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk
 
     DEBUG("%s bus %d: SPI_CLOCK_REG=%08x\n",
           __func__, bus, _spi[bus].regs->clock.val);
-
-    return SPI_OK;
 }
 
 void IRAM_ATTR spi_release(spi_t bus)
diff --git a/cpu/fe310/periph/spi.c b/cpu/fe310/periph/spi.c
index 9a7d0429ee..e880415b9f 100644
--- a/cpu/fe310/periph/spi.c
+++ b/cpu/fe310/periph/spi.c
@@ -22,9 +22,10 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "cpu.h"
 #include "mutex.h"
-#include "assert.h"
 #include "periph/spi.h"
 
 #include "vendor/spi.h"
@@ -102,7 +103,7 @@ int spi_init_cs(spi_t dev, spi_cs_t cs)
     return SPI_OK;
 }
 
-int spi_acquire(spi_t dev, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t dev, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     (void)cs;
     assert(dev < SPI_NUMOF);
@@ -111,8 +112,6 @@ int spi_acquire(spi_t dev, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 
     _REG32(spi_config[dev].addr, SPI_REG_SCKDIV) = _spi_clks_config[clk];
     _REG32(spi_config[dev].addr, SPI_REG_SCKMODE) = mode;
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t dev)
diff --git a/cpu/kinetis/periph/spi.c b/cpu/kinetis/periph/spi.c
index 6c9e8d1d65..52da320b2f 100644
--- a/cpu/kinetis/periph/spi.c
+++ b/cpu/kinetis/periph/spi.c
@@ -26,9 +26,10 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "cpu.h"
 #include "mutex.h"
-#include "assert.h"
 #include "periph/spi.h"
 
 #define ENABLE_DEBUG        0
@@ -144,9 +145,10 @@ int spi_init_cs(spi_t bus, spi_cs_t cs)
     return SPI_OK;
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
-    (void) cs;
+    (void)cs;
+    assert((unsigned)bus < SPI_NUMOF);
     /* lock and power on the bus */
     mutex_lock(&locks[bus]);
     poweron(bus);
@@ -156,8 +158,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 
     /* configure clock and mode */
     dev(bus)->CTAR[0] = (mode | SPI_CTAR_FMSZ(7) | spi_clk_config[clk]);
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/lm4f120/periph/spi.c b/cpu/lm4f120/periph/spi.c
index d8864e5c8e..319c896c18 100644
--- a/cpu/lm4f120/periph/spi.c
+++ b/cpu/lm4f120/periph/spi.c
@@ -67,9 +67,10 @@ void spi_init_pins(spi_t bus)
     ROM_GPIOPinTypeSSI(spi_confs[bus].gpio_port, spi_confs[bus].pins.mask);
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
-    (void) cs;
+    (void)cs;
+    assert((unsigned)bus < SPI_NUMOF);
     /* lock bus */
     mutex_lock(&locks[bus]);
     /* enable clock for SSI */
@@ -83,8 +84,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
                            8);
 
     ROM_SSIEnable(spi_confs[bus].ssi_base);
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/lpc23xx/periph/spi.c b/cpu/lpc23xx/periph/spi.c
index 17e226fc5b..4cf79e6a97 100644
--- a/cpu/lpc23xx/periph/spi.c
+++ b/cpu/lpc23xx/periph/spi.c
@@ -95,20 +95,17 @@ void spi_init_pins(spi_t bus)
     *(&PINSEL0 + cfg->pinsel_clk) |= cfg->pinsel_msk_clk;
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
-    (void) cs;
+    (void)cs; (void)mode;
+    assert((unsigned)bus < SPI_NUMOF);
+    assert(mode == SPI_MODE_0);
 
     uint32_t pclksel;
     uint32_t cpsr;
 
     lpc23xx_spi_t *dev = get_dev(bus);
 
-    /* only support for mode 0 at the moment */
-    if (mode != SPI_MODE_0) {
-        return SPI_NOMODE;
-    }
-
     /* lock bus */
     mutex_lock(&lock[bus]);
 
@@ -141,8 +138,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
     while (dev->SR & SSPSR_RNE) {       /* while RNE (Receive FIFO Not Empty)...*/
         dev->DR;                        /* read data*/
     }
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/msp430fxyz/periph/spi.c b/cpu/msp430fxyz/periph/spi.c
index e36831982b..34ccf7dd13 100644
--- a/cpu/msp430fxyz/periph/spi.c
+++ b/cpu/msp430fxyz/periph/spi.c
@@ -23,9 +23,10 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "cpu.h"
 #include "mutex.h"
-#include "assert.h"
 #include "periph/spi.h"
 
 /**
@@ -36,7 +37,7 @@ static mutex_t spi_lock = MUTEX_INIT;
 
 void spi_init(spi_t bus)
 {
-    assert(bus <= SPI_NUMOF);
+    assert((unsigned)bus < SPI_NUMOF);
 
 /* we need to differentiate between the legacy SPI device and USCI */
 #ifndef SPI_USE_USCI
@@ -66,14 +67,12 @@ void spi_init_pins(spi_t bus)
     gpio_periph_mode(SPI_PIN_CLK, true);
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     (void)bus;
     (void)cs;
-
-    if (clk == SPI_CLK_10MHZ) {
-        return SPI_NOCLK;
-    }
+    assert((unsigned)bus < SPI_NUMOF);
+    assert(clk != SPI_CLK_10MHZ);
 
     /* lock the bus */
     mutex_lock(&spi_lock);
@@ -100,8 +99,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
     /* release from software reset */
     SPI_BASE->CTL1 &= ~(USCI_SPI_CTL1_SWRST);
 #endif
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/native/periph/spidev_linux.c b/cpu/native/periph/spidev_linux.c
index a38ee8144b..4d439711d1 100644
--- a/cpu/native/periph/spidev_linux.c
+++ b/cpu/native/periph/spidev_linux.c
@@ -20,6 +20,7 @@
 
 #ifdef MODULE_PERIPH_SPIDEV_LINUX
 
+#include <assert.h>
 #include <fcntl.h>
 #include <string.h>
 #include <sys/ioctl.h>
@@ -145,12 +146,10 @@ void spidev_linux_teardown(void)
     }
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     DEBUG("spi_acquire(%u, %u, 0x%02x, %d)\n", bus, cs, mode, clk);
-    if (bus >= SPI_NUMOF) {
-        return SPI_NODEV;
-    }
+    assert((unsigned)bus < SPI_NUMOF);
 
     mutex_lock(&(device_state[bus].lock));
 
@@ -166,8 +165,7 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
         unsigned csid = CS_TO_CSID(cs);
         if (device_state[bus].fd[csid] < 0) {
             DEBUG("spi_acquire: No fd for %u:%u\n", bus, csid);
-            mutex_unlock(&(device_state[bus].lock));
-            return SPI_NOCS;
+            assert(0);
         }
         fd = device_state[bus].fd[csid];
         DEBUG("spi_acquire: Using %u:%u with HWCS (-> fd 0x%x)\n", bus, csid, fd);
@@ -175,25 +173,23 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
     else if (IS_GPIO_CS(cs) || cs == SPI_CS_UNDEF) {
         fd = spidev_get_first_fd(&(device_state[bus]));
         if (fd < 0) {
-            mutex_unlock(&(device_state[bus].lock));
-            return SPI_NOCS;
+            DEBUG("spi_acquire: Invalid CS parameter\n");
+            assert(0);
         }
         DEBUG("spi_acquire: Using SPI_CS_UNDEF (-> fd 0x%x)\n", fd);
     }
     else {
         DEBUG("spi_acquire: Invalid CS parameter\n");
-        mutex_unlock(&(device_state[bus].lock));
-        return SPI_NOCS;
+        assert(0);
     }
 
     int res = spi_set_params(fd, use_hwcs, mode, clk);
     if (res < 0) {
         DEBUG("spi_acquire: set_params failed\n");
-        mutex_unlock(&(device_state[bus].lock));
+        assert(0);
     }
 
     DEBUG("spi_acquire: bus %u acquired\n", bus);
-    return SPI_OK;
 }
 
 void spi_init(spi_t bus)
diff --git a/cpu/nrf51/periph/spi.c b/cpu/nrf51/periph/spi.c
index 48fea3424b..c3efd1e99d 100644
--- a/cpu/nrf51/periph/spi.c
+++ b/cpu/nrf51/periph/spi.c
@@ -21,9 +21,10 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "cpu.h"
 #include "mutex.h"
-#include "assert.h"
 #include "periph/spi.h"
 #include "periph/gpio.h"
 
@@ -59,9 +60,10 @@ void spi_init_pins(spi_t bus)
     SPI_MISOSEL = spi_config[bus].miso;
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
-    (void) cs;
+    (void)cs;
+    assert((unsigned)bus < SPI_NUMOF);
 
     mutex_lock(&locks[bus]);
     /* power on the bus (NRF51 only) */
@@ -71,8 +73,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
     dev(bus)->FREQUENCY = clk;
     /* enable the bus */
     dev(bus)->ENABLE = 1;
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/nrf52/periph/spi.c b/cpu/nrf52/periph/spi.c
index 9376409b37..3482d5ae17 100644
--- a/cpu/nrf52/periph/spi.c
+++ b/cpu/nrf52/periph/spi.c
@@ -24,9 +24,10 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "cpu.h"
 #include "mutex.h"
-#include "assert.h"
 #include "periph/spi.h"
 #include "periph/gpio.h"
 #include "periph_cpu.h"
@@ -147,9 +148,10 @@ void spi_init_pins(spi_t bus)
     spi_twi_irq_register_spi(dev(bus), spi_isr_handler, (void *)bus);
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     (void)cs;
+    assert((unsigned)bus < SPI_NUMOF);
 
     mutex_lock(&locks[bus]);
     /* configure bus */
@@ -157,8 +159,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
     dev(bus)->FREQUENCY = clk;
     /* enable the bus */
     dev(bus)->ENABLE = SPIM_ENABLE_ENABLE_Enabled;
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/qn908x/periph/spi.c b/cpu/qn908x/periph/spi.c
index 66dd689c17..ff4f114212 100644
--- a/cpu/qn908x/periph/spi.c
+++ b/cpu/qn908x/periph/spi.c
@@ -20,7 +20,8 @@
  * @}
  */
 
-#include "assert.h"
+#include <assert.h>
+
 #include "bitarithm.h"
 #include "mutex.h"
 
@@ -187,8 +188,10 @@ void spi_deinit_pins(spi_t bus)
 }
 #endif /* MODULE_PERIPH_SPI_RECONFIGURE */
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
+    assert((unsigned)bus < SPI_NUMOF);
+    assert((mode & ~(SPI_CFG_CPHA_MASK | SPI_CFG_CPOL_MASK)) == 0);
     const spi_conf_t *const conf = &spi_config[bus];
 
     mutex_lock(&locks[bus]);
@@ -197,18 +200,12 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
      * matter how far it is from the requested one. */
     _spi_controller_set_speed(conf->dev, clk);
 
-    if ((mode & ~(SPI_CFG_CPHA_MASK | SPI_CFG_CPOL_MASK)) != 0) {
-        return SPI_NOMODE;
-    }
-
     DEBUG("[spi] acquire: mode CPHA=%d CPOL=%d, cs=0x%" PRIx32 "\n",
           !!(mode & SPI_CFG_CPHA_MASK), !!(mode & SPI_CFG_CPOL_MASK),
           (uint32_t)cs);
 
     conf->dev->CFG =
         (conf->dev->CFG & ~(SPI_CFG_CPHA_MASK | SPI_CFG_CPOL_MASK)) | mode;
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/sam0_common/periph/spi.c b/cpu/sam0_common/periph/spi.c
index 9832763015..d7cd5803e9 100644
--- a/cpu/sam0_common/periph/spi.c
+++ b/cpu/sam0_common/periph/spi.c
@@ -26,9 +26,10 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "cpu.h"
 #include "mutex.h"
-#include "assert.h"
 #include "periph/spi.h"
 #include "pm_layered.h"
 
@@ -374,9 +375,10 @@ void spi_deinit_pins(spi_t bus)
     gpio_disable_mux(spi_config[bus].mosi_pin);
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
     (void)cs;
+    assert((unsigned)bus < SPI_NUMOF);
 
     /* get exclusive access to the device */
     mutex_lock(&locks[bus]);
@@ -392,8 +394,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 
     /* mux clk_pin to SPI peripheral */
     gpio_init_mux(spi_config[bus].clk_pin, spi_config[bus].clk_mux);
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/sam3/periph/spi.c b/cpu/sam3/periph/spi.c
index b551d9d660..e542519dab 100644
--- a/cpu/sam3/periph/spi.c
+++ b/cpu/sam3/periph/spi.c
@@ -23,9 +23,10 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "cpu.h"
 #include "mutex.h"
-#include "assert.h"
 #include "periph/gpio.h"
 #include "periph/spi.h"
 
@@ -62,9 +63,11 @@ void spi_init_pins(spi_t bus)
     gpio_init_mux(spi_config[bus].miso, spi_config[bus].mux);
 }
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
-    (void) cs;
+    (void)cs;
+    assert((unsigned)bus < SPI_NUMOF);
+
     /* lock bus */
     mutex_lock(&locks[bus]);
     /* enable SPI device clock */
@@ -73,8 +76,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
     dev(bus)->SPI_CSR[0] = (SPI_CSR_SCBR(CLOCK_CORECLOCK / clk) | mode);
     dev(bus)->SPI_MR = (SPI_MR_MSTR | SPI_MR_MODFDIS);
     dev(bus)->SPI_CR = SPI_CR_SPIEN;
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)
diff --git a/cpu/stm32/periph/spi.c b/cpu/stm32/periph/spi.c
index 762bb34179..7348c355c2 100644
--- a/cpu/stm32/periph/spi.c
+++ b/cpu/stm32/periph/spi.c
@@ -26,6 +26,8 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "bitarithm.h"
 #include "cpu.h"
 #include "mutex.h"
@@ -219,8 +221,9 @@ int spi_init_with_gpio_mode(spi_t bus, spi_gpio_mode_t mode)
 }
 #endif
 
-int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
 {
+    assert((unsigned)bus < SPI_NUMOF);
 
     /* lock bus */
     mutex_lock(&locks[bus]);
@@ -279,8 +282,6 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
     if (cr2_extra_settings) {
         dev(bus)->CR2 = (SPI_CR2_SETTINGS | cr2_extra_settings);
     }
-
-    return SPI_OK;
 }
 
 void spi_release(spi_t bus)