diff --git a/frontend/persist.lua b/frontend/persist.lua
index b2a559084..dfaf332df 100644
--- a/frontend/persist.lua
+++ b/frontend/persist.lua
@@ -82,11 +82,20 @@ local codecs = {
             if not ok then
                 return nil, "cannot serialize " .. tostring(t) .. " (" .. str .. ")"
             end
+
+            local cbuff, clen = zstd.zstd_compress(str, #str)
+
+            if not path then
+                local result = ffi.string(cbuff, clen)
+                C.free(cbuff)
+                return result, clen
+            end
+
             local f = C.fopen(path, "wb")
             if f == nil then
+                C.free(cbuff)
                 return nil, "fopen: " .. ffi.string(C.strerror(ffi.errno()))
             end
-            local cbuff, clen = zstd.zstd_compress(str, #str)
             if C.fwrite(cbuff, 1, clen, f) < clen then
                 C.fclose(f)
                 C.free(cbuff)
@@ -100,7 +109,19 @@ local codecs = {
             return true, clen
         end,
 
-        deserialize = function(path)
+        deserialize = function(str, path)
+            if str and not path then
+                local buff, ulen = zstd.zstd_uncompress(str, #str)
+                if not buff then
+                    return nil, "failed to decompress string"
+                end
+                local ok, t = pcall(buffer.decode, ffi.string(buff, ulen))
+                C.free(buff)
+                if not ok then
+                    return nil, "malformed serialized data (" .. t .. ")"
+                end
+                return t
+            end
             local f = C.fopen(path, "rb")
             if f == nil then
                 return nil, "fopen: " .. ffi.string(C.strerror(ffi.errno()))
@@ -124,9 +145,8 @@ local codecs = {
             local buff, ulen = zstd.zstd_uncompress(data, size)
             C.free(data)
 
-            local str = ffi.string(buff, ulen)
+            str = ffi.string(buff, ulen)
             C.free(buff)
-
             local ok, t = pcall(buffer.decode, str)
             if not ok then
                 return nil, "malformed serialized data (" .. t .. ")"
@@ -156,8 +176,11 @@ local codecs = {
             return content
         end,
 
-        deserialize = function(str)
-            local t, err = loadfile(str)
+        deserialize = function(str, path)
+            local t, err
+            if path then
+                t, err = loadfile(path)
+            end
             if not t then
                 t, err = loadstring(str)
             end
@@ -221,7 +244,7 @@ end
 function Persist:load()
     local t, err
     if codecs[self.codec].reads_from_file then
-        t, err = codecs[self.codec].deserialize(self.path)
+        t, err = codecs[self.codec].deserialize(nil, self.path)
     else
         local str
         str, err = readFile(self.path)
diff --git a/spec/unit/persist_spec.lua b/spec/unit/persist_spec.lua
index def52d643..0c04c1fd1 100644
--- a/spec/unit/persist_spec.lua
+++ b/spec/unit/persist_spec.lua
@@ -81,8 +81,7 @@ describe("Persist module", function()
 
     it("should return standalone serializers/deserializers", function()
         local tab = sample
-        -- NOTE: zstd only deser from a *file*, not a string.
-        for _, codec in ipairs({"dump", "serpent", "bitser", "luajit"}) do
+        for _, codec in ipairs({"dump", "serpent", "bitser", "luajit", "zstd"}) do
             assert.is_true(Persist.getCodec(codec).id == codec)
             local ser = Persist.getCodec(codec).serialize
             local deser = Persist.getCodec(codec).deserialize
@@ -91,7 +90,7 @@ describe("Persist module", function()
             if not t then
                 print(codec, "deser failed:", err)
             end
-            assert.are.same(t, tab)
+            assert.are.same(tab, t)
         end
     end)
 
@@ -101,7 +100,7 @@ describe("Persist module", function()
             local ser = Persist.getCodec(codec).serialize
             local deser = Persist.getCodec(codec).deserialize
             local str = ser(tab)
-            assert.are.same(deser(str), tab)
+            assert.are.same(tab, deser(str))
         end
     end)