diff --git a/src/transforms/serializer.js b/src/transforms/serializer.js
index 76f7ef27..ca22805d 100644
--- a/src/transforms/serializer.js
+++ b/src/transforms/serializer.js
@@ -11,6 +11,23 @@ const merge = require('lodash.merge')
 const minecraftData = require('minecraft-data')
 const protocols = {}
 
+// The generated code is fully determined by these versions plus the protocol
+// key and customPackets, so together they make a stale cache file unreachable.
+function protocolCacheFile (state, direction, version, customPackets) {
+  const cacheDir = process.env.NMP_PROTOCOL_CACHE_DIR ??
+    require('path').join(require('os').tmpdir(), 'node-minecraft-protocol-cache')
+  if (cacheDir === '0') return null
+  const inputs = [
+    require('../../package.json').version,
+    require('protodef/package.json').version,
+    require('minecraft-data/package.json').version,
+    JSON.stringify(customPackets ?? {})
+  ].join(';')
+  const hash = require('crypto').createHash('sha1').update(inputs).digest('hex').slice(0, 12)
+  const name = `${version}-${state}-${direction}-${hash}.js`.replace(/[^a-zA-Z0-9.-]/g, '_')
+  return require('path').join(cacheDir, name)
+}
+
 function createProtocol (state, direction, version, customPackets, compiled = true) {
   const key = `${state};${direction};${version}${compiled ? ';c' : ''}`
   if (protocols[key]) { return protocols[key] }
@@ -24,18 +41,31 @@ function createProtocol (state, direction, version, customPackets, compiled = tr
     throw new Error(`Unsupported protocol version '${versionInfo.version}' (attempted to use '${mcData.version.version}' data); try updating your packages with 'npm update'`)
   }
 
-  const mergedProtocol = merge(mcData.protocol, customPackets?.[mcData.version.majorVersion] ?? {})
-
   if (compiled) {
     const compiler = new ProtoDefCompiler()
     compiler.addTypes(require('../datatypes/compiler-minecraft'))
-    compiler.addProtocol(mergedProtocol, [state, direction])
     nbt.addTypesToCompiler('big', compiler)
-    const proto = compiler.compileProtoDefSync()
+    const cacheFile = protocolCacheFile(state, direction, version, customPackets)
+    let proto
+    if (cacheFile) {
+      // A hit also skips loading mcData.protocol and walking it in
+      // addProtocol, which cost as much as the compile itself.
+      try { proto = compiler.loadCompiledProtoDefSync(cacheFile) } catch {}
+    }
+    if (!proto) {
+      const mergedProtocol = merge(mcData.protocol, customPackets?.[mcData.version.majorVersion] ?? {})
+      compiler.addProtocol(mergedProtocol, [state, direction])
+      // Registered a second time: the nbt schemas must override the types the
+      // protocol declares as native (the pre-cache call above only provides
+      // the natives needed to load a cached protocol).
+      nbt.addTypesToCompiler('big', compiler)
+      proto = compiler.compileProtoDefSync(cacheFile ? { cacheFile } : {})
+    }
     protocols[key] = proto
     return proto
   }
 
+  const mergedProtocol = merge(mcData.protocol, customPackets?.[mcData.version.majorVersion] ?? {})
   const proto = new ProtoDef(false)
   proto.addTypes(minecraft)
   proto.addProtocol(mergedProtocol, [state, direction])