diff --git a/src/blockstore/v1/write.cpp b/src/blockstore/v1/write.cpp
index 433ed0eb..448dfbfd 100644
--- a/src/blockstore/v1/write.cpp
+++ b/src/blockstore/v1/write.cpp
@@ -183,7 +183,7 @@ bool blockstore_impl_t::enqueue_write(blockstore_op_t *op)
         uint32_t end = (op->offset+op->len-1) / dsk.csum_block_size;
         auto fn = state & BS_ST_BIG_WRITE ? crc32c_pad : crc32c_nopad;
         if (start == end)
-            data_csums[0] = fn(0, op->buf, op->len, op->offset - start*dsk.csum_block_size, end*dsk.csum_block_size - (op->offset+op->len));
+            data_csums[0] = fn(0, op->buf, op->len, op->offset - start*dsk.csum_block_size, (end+1)*dsk.csum_block_size - (op->offset+op->len));
         else
         {
             // First block
diff --git a/src/util/crc32c.c b/src/util/crc32c.c
index ab9da5f7..e3c9f71e 100644
--- a/src/util/crc32c.c
+++ b/src/util/crc32c.c
@@ -37,6 +37,7 @@
 #include <stdlib.h>
 #include <stdint.h>
 #include <unistd.h>
+#include <assert.h>
 #include "crc32c.h"
 
 #ifdef WITH_ISAL
@@ -394,6 +395,7 @@ static uint8_t zero_page[4096] = {};
 
 uint32_t crc32c_pad(uint32_t prev_crc, const void *buf, size_t len, size_t left_pad, size_t right_pad)
 {
+    assert(left_pad < 0x10000000 && right_pad < 0x10000000);
     uint32_t r = prev_crc;
     while (left_pad >= 4096)
     {