diff --git a/server/lib/mempool.ex b/server/lib/mempool.ex
index 6582f4b..4ae7b45 100644
--- a/server/lib/mempool.ex
+++ b/server/lib/mempool.ex
@@ -191,6 +191,7 @@ defmodule BitcoinStream.Mempool do
       :registered ->
         with [] <- :ets.lookup(:block_cache, txid) do # double check tx isn't included in the last block
           :ets.insert(:mempool_cache, {txid, { txn.inputs, txn.value + txn.fee, txn.inflated }, nil});
+          cache_spends(txid, txn.inputs);
           get(pid)
         else
           _ ->
@@ -248,6 +249,7 @@ defmodule BitcoinStream.Mempool do
           [{_txid, _, txn}] when txn != nil ->
             :ets.insert(:mempool_cache, {txid, { txn.inputs, txn.value + txn.fee, txn.inflated }, nil});
             :ets.delete(:sync_cache, txid);
+            cache_spends(txid, txn.inputs);
             if do_count do
               increment(pid);
             end
@@ -295,8 +297,10 @@ defmodule BitcoinStream.Mempool do
         get(pid)
 
       # tx fully processed and not already dropped
-      [{_txid, data, _status}] when data != nil ->
+      [{txid, data, _status}] when data != nil ->
         :ets.delete(:mempool_cache, txid);
+        {inputs, _value, _inflated} = data;
+        uncache_spends(inputs);
         decrement(pid);
         get(pid)
 
@@ -429,6 +433,7 @@ defmodule BitcoinStream.Mempool do
               inflated_txn <- BitcoinTx.inflate(txn, false) do
           if inflated_txn.inflated do
             :ets.insert(:mempool_cache, {txid, { inflated_txn.inputs, inflated_txn.value + inflated_txn.fee, inflated_txn.inflated }, status});
+            cache_spends(txid, inflated_txn.inputs);
             Logger.debug("repaired #{repaired} mempool txns #{txid}");
             repaired + 1
           else
@@ -493,4 +498,32 @@ defmodule BitcoinStream.Mempool do
     end
   end
 
+
+  defp cache_spend(txid, index, input) do
+    :ets.insert(:spend_cache, {[input.prev_txid, input.prev_vout], [txid, index]})
+  end
+  defp cache_spends(_txid, _index, []) do
+    :ok
+  end
+  defp cache_spends(txid, index, [input | rest]) do
+    cache_spend(txid, index, input);
+    cache_spends(txid, index + 1, rest)
+  end
+  defp cache_spends(txid, inputs) do
+    cache_spends(txid, 0, inputs)
+  end
+
+  defp uncache_spend(input) do
+    :ets.delete(:spend_cache, [input.prev_txid, input.prev_vout])
+  end
+  defp uncache_spends([]) do
+    :ok
+  end
+  defp uncache_spends([input | rest]) do
+    uncache_spend(input);
+    uncache_spends(rest)
+  end
+  defp uncache_spends(inputs) do
+    uncache_spends(inputs)
+  end
 end
diff --git a/server/lib/spend_index.ex b/server/lib/spend_index.ex
index 33c2727..0c11095 100644
--- a/server/lib/spend_index.ex
+++ b/server/lib/spend_index.ex
@@ -5,6 +5,7 @@ defmodule BitcoinStream.Index.Spend do
   use GenServer
 
   alias BitcoinStream.Protocol.Block, as: BitcoinBlock
+  alias BitcoinStream.Protocol.Transaction, as: BitcoinTx
   alias BitcoinStream.RPC, as: RPC
 
   def start_link(opts) do
@@ -15,6 +16,7 @@ defmodule BitcoinStream.Index.Spend do
 
   @impl true
   def init([indexed]) do
+    :ets.new(:spend_cache, [:set, :public, :named_table]);
     if (indexed != nil) do
       {:ok, dbref} = :rocksdb.open(String.to_charlist("data/index/spend"), [create_if_missing: true]);
       Process.send_after(self(), :sync, 2000);
@@ -205,7 +207,7 @@ defmodule BitcoinStream.Index.Spend do
   defp index_block_inputs(dbref, batch, txns) do
     spends = index_txs(txns, %{});
     Enum.each(spends, fn {binid, outputs} ->
-      case get_spends(dbref, binid) do
+      case get_chain_spends(dbref, binid) do
         false ->
           Logger.error("uninitialised tx in input index: #{Base.encode16(binid, [case: :lower])}")
           :ok
@@ -294,13 +296,22 @@ defmodule BitcoinStream.Index.Spend do
     end
   end
 
-  defp get_spends(dbref, binary_txid) do
+  defp get_chain_spends(dbref, binary_txid) do
     case :rocksdb.get(dbref, binary_txid, []) do
       {:ok, spends} ->
         spends
 
       :not_found ->
-        false
+        # uninitialized, try to construct on-the-fly from RPC data
+        txid = Base.encode16(binary_txid);
+        with {:ok, 200, hextx} <- RPC.request(:rpc, "getrawtransaction", [txid]),
+             rawtx <- Base.decode16!(hextx, case: :lower),
+             {:ok, tx } <- BitcoinTx.decode(rawtx) do
+          size = length(tx.outputs) * 35 * 8;
+          <<0::integer-size(size)>>
+        else
+          _ -> false
+        end
 
       _ ->
         Logger.error("unexpected leveldb response");
@@ -308,16 +319,19 @@ defmodule BitcoinStream.Index.Spend do
     end
   end
 
-  defp unpack_spends(<<>>, spend_array) do
-    Enum.reverse(spend_array)
+  defp unpack_spends(<<>>, spend_list) do
+    Enum.reverse(spend_list)
   end
   # unspent outputs are zeroed out
-  defp unpack_spends(<<0::integer-size(280), rest::binary>>, spend_array) do
-    unpack_spends(rest, [false | spend_array])
+  defp unpack_spends(<<0::integer-size(280), rest::binary>>, spend_list) do
+    unpack_spends(rest, [false | spend_list])
   end
-  defp unpack_spends(<<binary_txid::binary-size(32), index::integer-size(24), rest::binary>>, spend_array) do
+  defp unpack_spends(<<binary_txid::binary-size(32), index::integer-size(24), rest::binary>>, spend_list) do
     txid = Base.encode16(binary_txid, [case: :lower]);
-    unpack_spends(rest, [[txid, index] | spend_array])
+    unpack_spends(rest, [[txid, index] | spend_list])
+  end
+  defp unpack_spends(false) do
+    []
   end
   defp unpack_spends(bin) do
     unpack_spends(bin, [])
@@ -325,15 +339,30 @@ defmodule BitcoinStream.Index.Spend do
 
   defp get_transaction_spends(dbref, txid) do
     binary_txid = Base.decode16!(txid, [case: :lower]);
-    case get_spends(dbref, binary_txid) do
-      false ->
-        {:ok, nil}
+    chain_spends = get_chain_spends(dbref, binary_txid);
+    spend_list = unpack_spends(chain_spends);
+    spend_list = add_mempool_spends(txid, spend_list);
+    {:ok, spend_list}
+  end
 
-      spends ->
-        spend_array = unpack_spends(spends);
-        {:ok, spend_array}
+  defp add_mempool_spends(_txid, _index, [],  added) do
+    Enum.reverse(added)
+  end
+  defp add_mempool_spends(txid, index, [false | rest], added) do
+    case :ets.lookup(:spend_cache, [txid, index]) do
+      [] ->
+        add_mempool_spends(txid, index + 1, rest, [false | added])
+
+      [{[_index, _txid], spend}] ->
+        add_mempool_spends(txid, index + 1, rest, [spend | added])
     end
   end
+  defp add_mempool_spends(txid, index, [spend | rest], added) do
+    add_mempool_spends(txid, index + 1, rest, [spend | added])
+  end
+  defp add_mempool_spends(txid, spend_list) do
+    add_mempool_spends(txid, 0, spend_list, [])
+  end
 
   defp stack_dropped_blocks(dbref, hash, undo_stack, min_height) do
     # while we're below the latest processed height
@@ -351,7 +380,7 @@ defmodule BitcoinStream.Index.Spend do
   defp drop_block_inputs(dbref, batch, txns) do
     spends = index_txs(txns, %{});
     Enum.each(spends, fn {binid, outputs} ->
-      case get_spends(dbref, binid) do
+      case get_chain_spends(dbref, binid) do
         false ->
           Logger.error("uninitialised tx in input index: #{Base.encode16(binid, [case: :lower])}")
           :ok