diff --git a/src/spislave.cpp b/src/spislave.cpp
index 6df563b1..bbcb677d 100644
--- a/src/spislave.cpp
+++ b/src/spislave.cpp
@@ -35,7 +35,9 @@ static const char TAG[] = __FILE__;
 // https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/peripherals/spi_slave.html
 #define BUFFER_SIZE                                                            \
   (MAX(8, HEADER_SIZE + PAYLOAD_BUFFER_SIZE) +                                 \
-   (4 - MAX(8, HEADER_SIZE + PAYLOAD_BUFFER_SIZE) % 4))
+   (PAYLOAD_BUFFER_SIZE % 4 == 0                                               \
+        ? 0                                                                    \
+        : 4 - MAX(8, HEADER_SIZE + PAYLOAD_BUFFER_SIZE) % 4))
 DMA_ATTR uint8_t txbuf[BUFFER_SIZE];
 DMA_ATTR uint8_t rxbuf[BUFFER_SIZE];
 
@@ -70,7 +72,11 @@ void spi_slave_task(void *param) {
 
     // set length for spi slave driver
     transaction_size = HEADER_SIZE + msg.MessageSize;
-    transaction_size += (4 - transaction_size % 4);
+    // SPI transaction size needs to be at least 8 bytes and dividable by 4, see
+    // https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/peripherals/spi_slave.html
+    if (transaction_size % 4 != 0) {
+      transaction_size += (4 - transaction_size % 4);
+    }
 
     // prepare spi transaction
     spi_slave_transaction_t spi_transaction = {0};