diff --git a/drivers/thunderbolt/dma_port.c b/drivers/thunderbolt/dma_port.c
index 847dd07a7b17..de219953c8b3 100644
--- a/drivers/thunderbolt/dma_port.c
+++ b/drivers/thunderbolt/dma_port.c
@@ -364,15 +364,15 @@ int dma_port_flash_read(struct tb_dma_port *dma, unsigned int address,
 			void *buf, size_t size)
 {
 	unsigned int retries = DMA_PORT_RETRIES;
-	unsigned int offset;
-
-	offset = address & 3;
-	address = address & ~3;
 
 	do {
-		u32 nbytes = min_t(u32, size, MAIL_DATA_DWORDS * 4);
+		unsigned int offset;
+		size_t nbytes;
 		int ret;
 
+		offset = address & 3;
+		nbytes = min_t(size_t, size + offset, MAIL_DATA_DWORDS * 4);
+
 		ret = dma_port_flash_read_block(dma, address, dma->buf,
 						ALIGN(nbytes, 4));
 		if (ret) {
@@ -384,6 +384,7 @@ int dma_port_flash_read(struct tb_dma_port *dma, unsigned int address,
 			return ret;
 		}
 
+		nbytes -= offset;
 		memcpy(buf, dma->buf + offset, nbytes);
 
 		size -= nbytes;