diff --git a/src/liblzma/common/block_util.c b/src/liblzma/common/block_util.c
index 1dccacf..fa25b9a 100644
--- a/src/liblzma/common/block_util.c
+++ b/src/liblzma/common/block_util.c
@@ -58,7 +58,7 @@ lzma_block_unpadded_size(const lzma_block *block)
 	// NOTE: This function is used for validation too, so it is
 	// essential that these checks are always done even if
 	// Compressed Size is unknown.
-	if (block->version != 0
+	if (block == NULL || block->version != 0
 			|| block->header_size < LZMA_BLOCK_HEADER_SIZE_MIN
 			|| block->header_size > LZMA_BLOCK_HEADER_SIZE_MAX
 			|| (block->header_size & 3)