diff --git a/src/cljam/io/cram.clj b/src/cljam/io/cram.clj
index adebc32a..9889261d 100644
--- a/src/cljam/io/cram.clj
+++ b/src/cljam/io/cram.clj
@@ -374,7 +374,9 @@
                :rnext (get-in cram-header [:SQ (NS) :SN])
                :pnext (NP)
                :tlen (TS)))
-      (assoc record ::nf (NF)))))
+      (cond-> record
+        (pos? (bit-and (long flag) 0x04))
+        (assoc ::next-fragment (NF))))))
 
 (defn build-auxiliary-tags-decoder [{:keys [preservation-map]} {:keys [TL]} tag-decoders]
   (let [tag-dict (:TD preservation-map)]
@@ -388,29 +390,9 @@
                      [])
              (assoc record :options))))))
 
-(defn record-end [{:keys [pos ::len]} features]
-  (->> features
-       ^long (reduce
-              (fn [^long ret f]
-                (case (:code f)
-                  (:insertion :softclip)
-                  (- ret (alength ^bytes (:bases f)))
-
-                  (:deletion :ref-skip)
-                  (+ ret (long (:len f)))
-
-                  :insert-base
-                  (dec ret)
-
-                  ret))
-              len)
-       dec
-       (+ (long pos))))
-
 (defn record-seq
-  [seq-reader {:keys [preservation-map]} {:keys [rname pos ::len] :as record} features]
-  (let [end (record-end record features)
-        region {:chr rname :start pos :end end}
+  [seq-reader {:keys [preservation-map]} {:keys [rname pos ::end ::len]} features]
+  (let [region {:chr rname :start pos :end end}
         ref-bases (.getBytes ^String (cseq/read-sequence seq-reader region))
         bs (byte-array len (byte (int \N)))
         subst (:SM preservation-map)]
@@ -500,6 +482,25 @@
                    (conj! [(- read-len pos) \M]))]
         (some->> (not-empty (persistent! acc')) sam.cigar/simplify)))))
 
+(defn record-end [{:keys [pos ::len]} features]
+  (->> features
+       ^long (reduce
+              (fn [^long ret f]
+                (case (:code f)
+                  (:insertion :softclip)
+                  (- ret (alength ^bytes (:bases f)))
+
+                  (:deletion :ref-skip)
+                  (+ ret (long (:len f)))
+
+                  :insert-base
+                  (dec ret)
+
+                  ret))
+              len)
+       dec
+       (+ (long pos))))
+
 (defn build-mapped-read-decoder
   [seq-reader
    compression-header
@@ -509,10 +510,12 @@
            prev-pos 0
            fs (transient [])]
       (if (zero? i)
-        (let [features (persistent! fs)]
-          (assoc record
-                 :seq (record-seq seq-reader compression-header record features)
-                 :qual (record-qual record features decoders)
+        (let [features (persistent! fs)
+              end (record-end record features)
+              record' (assoc record ::end end)]
+          (assoc record'
+                 :seq (record-seq seq-reader compression-header record' features)
+                 :qual (record-qual record' features decoders)
                  :mapq (MQ)
                  :cigar (->> (or (features->cigar len features)
                                  [[len \M]])
@@ -571,6 +574,44 @@
           (mr-decoder record')
           (ur-decoder record'))))))
 
+(defn update-next-mate
+  [{:keys [^long flag] :as record} {^long mate-flag :flag :as mate}]
+  (assoc record
+         :flag (cond-> flag
+                 (pos? (bit-and mate-flag 0x10))
+                 (bit-or 0x20)
+
+                 (pos? (bit-and mate-flag 0x08))
+                 (bit-or 0x08))
+         :rnext (:rname mate)
+         :pnext (:pos mate)))
+
+(defn update-mate-records
+  [{^long s1 :pos ^long e1 ::end :as r1} {^long s2 :pos ^long e2 ::end :as r2}]
+  (let [r1' (update-next-mate r1 r2)
+        r2' (update-next-mate r2 r1)]
+    (if (or (pos? (bit-and (long (:flag r1)) 0x04))
+            (pos? (bit-and (long (:flag r2)) 0x04))
+            (not= (:rname r1') (:rname r2')))
+      [(assoc r1' :tlen 0) (assoc r2' :tlen 0)]
+      (if (<= s1 s2)
+        (let [tlen (inc (- e2 s1))]
+          [(assoc r1' :tlen tlen)
+           (assoc r2' :tlen (- tlen))])
+        (let [tlen (inc (- e1 s2))]
+          [(assoc r1' :tlen (- tlen))
+           (assoc r2' :tlen tlen)])))))
+
+(defn resolve-mate-records [^objects records]
+  (dotimes [i (alength records)]
+    (let [record (aget records i)]
+      (when-let [nf (::next-fragment record)]
+        (let [j (inc (+ i (long nf)))
+              mate (aget records j)
+              [record' mate'] (update-mate-records record mate)]
+          (aset records i record')
+          (aset records j mate'))))))
+
 (defn decode-slice-records [seq-reader cram-header compression-header slice-header blocks]
   (let [decoders (build-data-series-decoders (:data-series compression-header) blocks)
         tag-decoders (build-tag-decoders compression-header blocks)
@@ -579,9 +620,10 @@
                                                   compression-header
                                                   slice-header
                                                   decoders
-                                                  tag-decoders)]
-    (letfn [(step [^long i]
-              (when (pos? i)
-                (cons (record-decoder) (lazy-seq (step (dec i))))))]
-      (step (:records slice-header)))))
-
+                                                  tag-decoders)
+        n (:records slice-header)
+        records (object-array n)]
+    (dotimes [i n]
+      (aset records i (record-decoder)))
+    (resolve-mate-records records)
+    (map #(dissoc % ::flag ::len ::next-fragment) records)))