diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap_micro.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap_micro.c
index 75b43a6f88da..cf992220ece6 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap_micro.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap_micro.c
@@ -181,10 +181,11 @@ mze_compare(const void *arg1, const void *arg2)
 	return (0);
 }
 
-static void
+static int
 mze_insert(zap_t *zap, int chunkid, uint64_t hash, mzap_ent_phys_t *mzep)
 {
 	mzap_ent_t *mze;
+	avl_index_t idx;
 
 	ASSERT(zap->zap_ismicro);
 	ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
@@ -194,7 +195,12 @@ mze_insert(zap_t *zap, int chunkid, uint64_t hash, mzap_ent_phys_t *mzep)
 	mze->mze_chunkid = chunkid;
 	mze->mze_hash = hash;
 	mze->mze_phys = *mzep;
-	avl_add(&zap->zap_m.zap_avl, mze);
+	if (avl_find(&zap->zap_m.zap_avl, mze, &idx) != NULL) {
+		kmem_free(mze, sizeof (mzap_ent_t));
+		return (EEXIST);
+	}
+	avl_insert(&zap->zap_m.zap_avl, mze, idx);
+	return (0);
 }
 
 static mzap_ent_t *
@@ -329,10 +335,15 @@ mzap_open(objset_t *os, uint64_t obj, dmu_buf_t *db)
 			if (mze->mze_name[0]) {
 				zap_name_t *zn;
 
-				zap->zap_m.zap_num_entries++;
 				zn = zap_name_alloc(zap, mze->mze_name,
 				    MT_EXACT);
-				mze_insert(zap, i, zn->zn_hash, mze);
+				if (mze_insert(zap, i, zn->zn_hash, mze) == 0)
+					zap->zap_m.zap_num_entries++;
+				else {
+					printf("ZFS WARNING: Duplicated ZAP "
+					    "entry detected (%s).",
+					    mze->mze_name);
+				}
 				zap_name_free(zn);
 			}
 		}
@@ -771,7 +782,7 @@ mzap_addent(zap_name_t *zn, uint64_t value)
 			if (zap->zap_m.zap_alloc_next ==
 			    zap->zap_m.zap_num_chunks)
 				zap->zap_m.zap_alloc_next = 0;
-			mze_insert(zap, i, zn->zn_hash, mze);
+			VERIFY(0 == mze_insert(zap, i, zn->zn_hash, mze));
 			return;
 		}
 	}