diff --git a/src/commonlib/device_tree.c b/src/commonlib/device_tree.c
index fb1e78f590..a6fdd0cb61 100644
--- a/src/commonlib/device_tree.c
+++ b/src/commonlib/device_tree.c
@@ -766,13 +766,13 @@ bool fdt_is_valid(const void *blob)
 
 struct device_tree *fdt_unflatten(const void *blob)
 {
-	struct device_tree *tree = xzalloc(sizeof(*tree));
-	const struct fdt_header *header = (const struct fdt_header *)blob;
-	tree->header = header;
-
 	if (!fdt_is_valid(blob))
 		return NULL;
 
+	const struct fdt_header *header = blob;
+	struct device_tree *tree = xzalloc(sizeof(*tree));
+	tree->header = header;
+
 	uint32_t struct_offset = be32toh(header->structure_offset);
 	uint32_t strings_offset = be32toh(header->strings_offset);
 	uint32_t reserve_offset = be32toh(header->reserve_map_offset);