diff --git a/include/sys/zap_impl.h b/include/sys/zap_impl.h
index 6c72cd977c8..ea8963f550f 100644
--- a/include/sys/zap_impl.h
+++ b/include/sys/zap_impl.h
@@ -62,8 +62,9 @@ typedef struct mzap_phys {
 	uint64_t mz_salt;
 	uint64_t mz_normflags;
 	uint64_t mz_pad[5];
-	mzap_ent_phys_t mz_chunk[1];
+
 	/* actually variable size depending on block size */
+	mzap_ent_phys_t mz_chunk[];
 } mzap_phys_t;
 
 typedef struct mzap_ent {