diff --git a/extra/forestdb/lib/lib-tests.factor b/extra/forestdb/lib/lib-tests.factor
index 62b84c3a07..f00b80a9db 100644
--- a/extra/forestdb/lib/lib-tests.factor
+++ b/extra/forestdb/lib/lib-tests.factor
@@ -27,6 +27,9 @@ IN: forestdb.lib
 : set-kv-n ( n -- )
     make-kv-n [ fdb-set-kv ] assoc-each ;
 
+: del-kv-n ( n -- )
+    make-kv-n keys [ fdb-del-kv ] each ;
+
 : set-kv-nth ( n -- )
     make-kv-nth fdb-set-kv ;
 
@@ -363,7 +366,38 @@ IN: forestdb.lib
             0 10 [
                 [ seqnum>> ]
                 [ [ key>> ] [ keylen>> ] bi alien/length>string ] bi 2array ,
-            ] with-fdb-byseq-iterator
+            ] with-fdb-byseq-each
         ] { } make
     ] with-forestdb-path
 ] unit-test
+
+! Test byseq mapping
+{
+    V{ 1 2 3 4 5 }
+} [
+    delete-test-db-1
+    test-db-1 [
+        5 set-kv-n
+        fdb-commit-normal
+        0 10 [
+            fdb_doc>doc
+        ] with-fdb-byseq-map
+        [ seqnum>> ] map
+    ] with-forestdb-path
+] unit-test
+
+! Deleting 5 keys gives you 5 new seqnums that are those docs, but deleted
+{
+    V{ { 6 t } { 7 t } { 8 t } { 9 t } { 10 t } }
+} [
+    delete-test-db-1
+    test-db-1 [
+        5 set-kv-n
+        5 del-kv-n
+        fdb-commit-normal
+        0 10 [
+            fdb_doc>doc
+        ] with-fdb-byseq-map
+        [ [ seqnum>> ] [ deleted?>> ] bi 2array ] map
+    ] with-forestdb-path
+] unit-test
diff --git a/extra/forestdb/lib/lib.factor b/extra/forestdb/lib/lib.factor
index 730ae7de36..4d44ee44bc 100644
--- a/extra/forestdb/lib/lib.factor
+++ b/extra/forestdb/lib/lib.factor
@@ -333,6 +333,24 @@ T{ doc
         ] curry loop
     ] with-destructors ; inline
 
+<PRIVATE
+
+: collector-for-when ( quot exemplar -- quot' vec )
+    [ length ] keep new-resizable [ [ over [ push ] [ 2drop ] if ] curry compose ] keep ; inline
+
+: collector-when ( quot -- quot' vec )
+    V{ } collector-for-when ; inline
+
+PRIVATE>
+
+: with-fdb-map ( start-key end-key fdb_iterator_opt_t iterator-init iterator-next quot: ( obj -- ) -- )
+    [ execute ] 2dip
+    '[
+        _ &dispose handle>> [
+            _ execute [ _ with-doc t ] [ f f ] if* swap
+        ] curry collector-when [ loop ] dip
+    ] with-destructors ; inline
+
 : with-fdb-normal-iterator ( start-key end-key quot -- )
     [ FDB_ITR_NONE \ fdb-iterator-init \ fdb-iterator-next ] dip
     with-fdb-iterator ; inline
@@ -341,10 +359,14 @@ T{ doc
     [ FDB_ITR_NONE \ fdb-iterator-init \ fdb-iterator-next-meta-only ] dip
     with-fdb-iterator ; inline
 
-: with-fdb-byseq-iterator ( start-seq end-seq quot -- )
+: with-fdb-byseq-each ( start-seq end-seq quot -- )
     [ FDB_ITR_NONE \ fdb-iterator-byseq-init \ fdb-iterator-next-meta-only ] dip
     with-fdb-iterator ; inline
 
+: with-fdb-byseq-map ( start-seq end-seq quot -- )
+    [ FDB_ITR_NONE \ fdb-iterator-byseq-init \ fdb-iterator-next-meta-only ] dip
+    with-fdb-map ; inline
+
 ! Do not try to commit here, as it will fail with FDB_RESULT_RONLY_VIOLATION
 ! fdb-current is weird, it gets replaced if you call fdb-rollback
 ! Therefore, only clean up fdb-current once, and clean it up at the end