diff --git a/include/sys/arc.h b/include/sys/arc.h
index 6328392bee23..215c75b6dfa3 100644
--- a/include/sys/arc.h
+++ b/include/sys/arc.h
@@ -125,15 +125,15 @@ typedef struct arc_buf_info {
 
 void arc_space_consume(uint64_t space, arc_space_type_t type);
 void arc_space_return(uint64_t space, arc_space_type_t type);
-arc_buf_t *arc_buf_alloc(spa_t *spa, int size, void *tag,
+arc_buf_t *arc_buf_alloc(spa_t *spa, uint64_t size, void *tag,
     arc_buf_contents_t type);
-arc_buf_t *arc_loan_buf(spa_t *spa, int size);
+arc_buf_t *arc_loan_buf(spa_t *spa, uint64_t size);
 void arc_return_buf(arc_buf_t *buf, void *tag);
 void arc_loan_inuse_buf(arc_buf_t *buf, void *tag);
 void arc_buf_add_ref(arc_buf_t *buf, void *tag);
 boolean_t arc_buf_remove_ref(arc_buf_t *buf, void *tag);
 void arc_buf_info(arc_buf_t *buf, arc_buf_info_t *abi, int state_index);
-int arc_buf_size(arc_buf_t *buf);
+uint64_t arc_buf_size(arc_buf_t *buf);
 void arc_release(arc_buf_t *buf, void *tag);
 int arc_released(arc_buf_t *buf);
 void arc_buf_sigsegv(int sig, siginfo_t *si, void *unused);
diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index 2c7abe6ec542..408388aaff43 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -1434,12 +1434,12 @@ arc_space_return(uint64_t space, arc_space_type_t type)
 }
 
 arc_buf_t *
-arc_buf_alloc(spa_t *spa, int size, void *tag, arc_buf_contents_t type)
+arc_buf_alloc(spa_t *spa, uint64_t size, void *tag, arc_buf_contents_t type)
 {
 	arc_buf_hdr_t *hdr;
 	arc_buf_t *buf;
 
-	ASSERT3U(size, >, 0);
+	VERIFY3U(size, <=, SPA_MAXBLOCKSIZE);
 	hdr = kmem_cache_alloc(hdr_cache, KM_PUSHPAGE);
 	ASSERT(BUF_EMPTY(hdr));
 	hdr->b_size = size;
@@ -1477,7 +1477,7 @@ static char *arc_onloan_tag = "onloan";
  * freed.
  */
 arc_buf_t *
-arc_loan_buf(spa_t *spa, int size)
+arc_loan_buf(spa_t *spa, uint64_t size)
 {
 	arc_buf_t *buf;
 
@@ -1837,7 +1837,7 @@ arc_buf_remove_ref(arc_buf_t *buf, void* tag)
 	return (no_callback);
 }
 
-int
+uint64_t
 arc_buf_size(arc_buf_t *buf)
 {
 	return (buf->b_hdr->b_size);
@@ -3307,6 +3307,12 @@ arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp, arc_done_func_t *done,
 		enum zio_compress b_compress = ZIO_COMPRESS_OFF;
 		uint64_t b_asize = 0;
 
+		/* Gracefully handle a damaged logical block size. */
+		if (size > SPA_MAXBLOCKSIZE) {
+			rc = ECKSUM;
+			goto out;
+		}
+
 		if (hdr == NULL) {
 			/* this block is not in the cache */
 			arc_buf_hdr_t *exists = NULL;