diff --git a/.changeset/forty-walls-fry.md b/.changeset/forty-walls-fry.md
new file mode 100644
index 0000000000000..8eb4ac6e037ca
--- /dev/null
+++ b/.changeset/forty-walls-fry.md
@@ -0,0 +1,5 @@
+---
+'@eth-optimism/proxyd': patch
+---
+
+Add customizable whitelist error
diff --git a/proxyd/config.go b/proxyd/config.go
index ba60d67defd92..466deb9231b62 100644
--- a/proxyd/config.go
+++ b/proxyd/config.go
@@ -96,18 +96,19 @@ type BackendGroupsConfig map[string]*BackendGroupConfig
 type MethodMappingsConfig map[string]string
 
 type Config struct {
-	WSBackendGroup    string              `toml:"ws_backend_group"`
-	Server            ServerConfig        `toml:"server"`
-	Cache             CacheConfig         `toml:"cache"`
-	Redis             RedisConfig         `toml:"redis"`
-	Metrics           MetricsConfig       `toml:"metrics"`
-	RateLimit         RateLimitConfig     `toml:"rate_limit"`
-	BackendOptions    BackendOptions      `toml:"backend"`
-	Backends          BackendsConfig      `toml:"backends"`
-	Authentication    map[string]string   `toml:"authentication"`
-	BackendGroups     BackendGroupsConfig `toml:"backend_groups"`
-	RPCMethodMappings map[string]string   `toml:"rpc_method_mappings"`
-	WSMethodWhitelist []string            `toml:"ws_method_whitelist"`
+	WSBackendGroup        string              `toml:"ws_backend_group"`
+	Server                ServerConfig        `toml:"server"`
+	Cache                 CacheConfig         `toml:"cache"`
+	Redis                 RedisConfig         `toml:"redis"`
+	Metrics               MetricsConfig       `toml:"metrics"`
+	RateLimit             RateLimitConfig     `toml:"rate_limit"`
+	BackendOptions        BackendOptions      `toml:"backend"`
+	Backends              BackendsConfig      `toml:"backends"`
+	Authentication        map[string]string   `toml:"authentication"`
+	BackendGroups         BackendGroupsConfig `toml:"backend_groups"`
+	RPCMethodMappings     map[string]string   `toml:"rpc_method_mappings"`
+	WSMethodWhitelist     []string            `toml:"ws_method_whitelist"`
+	WhitelistErrorMessage string              `toml:"whitelist_error_message"`
 }
 
 func ReadFromEnvOrConfig(value string) (string, error) {
diff --git a/proxyd/integration_tests/testdata/whitelist.toml b/proxyd/integration_tests/testdata/whitelist.toml
index 55b118c38f62a..4a65248d71628 100644
--- a/proxyd/integration_tests/testdata/whitelist.toml
+++ b/proxyd/integration_tests/testdata/whitelist.toml
@@ -1,3 +1,5 @@
+whitelist_error_message = "rpc method is not whitelisted custom message"
+
 [server]
 rpc_port = 8545
 
diff --git a/proxyd/integration_tests/testdata/ws.toml b/proxyd/integration_tests/testdata/ws.toml
index f86b22f270546..4642e6bc0fc90 100644
--- a/proxyd/integration_tests/testdata/ws.toml
+++ b/proxyd/integration_tests/testdata/ws.toml
@@ -1,3 +1,5 @@
+whitelist_error_message = "rpc method is not whitelisted"
+
 ws_backend_group = "main"
 
 ws_method_whitelist = [
diff --git a/proxyd/integration_tests/validation_test.go b/proxyd/integration_tests/validation_test.go
index be964c14d0d71..6f0653df2c0e8 100644
--- a/proxyd/integration_tests/validation_test.go
+++ b/proxyd/integration_tests/validation_test.go
@@ -10,7 +10,7 @@ import (
 )
 
 const (
-	notWhitelistedResponse        = `{"jsonrpc":"2.0","error":{"code":-32001,"message":"rpc method is not whitelisted"},"id":999}`
+	notWhitelistedResponse        = `{"jsonrpc":"2.0","error":{"code":-32001,"message":"rpc method is not whitelisted custom message"},"id":999}`
 	parseErrResponse              = `{"jsonrpc":"2.0","error":{"code":-32700,"message":"parse error"},"id":null}`
 	invalidJSONRPCVersionResponse = `{"error":{"code":-32601,"message":"invalid JSON-RPC version"},"id":null,"jsonrpc":"2.0"}`
 	invalidIDResponse             = `{"error":{"code":-32601,"message":"invalid ID"},"id":null,"jsonrpc":"2.0"}`
diff --git a/proxyd/integration_tests/ws_test.go b/proxyd/integration_tests/ws_test.go
index d93d3a7562485..9ae12abdcbf83 100644
--- a/proxyd/integration_tests/ws_test.go
+++ b/proxyd/integration_tests/ws_test.go
@@ -7,6 +7,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/ethereum/go-ethereum/log"
+
 	"github.com/ethereum-optimism/optimism/proxyd"
 	"github.com/gorilla/websocket"
 	"github.com/stretchr/testify/require"
@@ -42,6 +44,13 @@ func TestConcurrentWSPanic(t *testing.T) {
 	require.NoError(t, err)
 	defer shutdown()
 
+	// suppress tons of log messages
+	oldHandler := log.Root().GetHandler()
+	log.Root().SetHandler(log.DiscardHandler())
+	defer func() {
+		log.Root().SetHandler(oldHandler)
+	}()
+
 	<-readyCh
 
 	var wg sync.WaitGroup
diff --git a/proxyd/proxyd.go b/proxyd/proxyd.go
index e9bbe42fc75f4..af9f44eb73197 100644
--- a/proxyd/proxyd.go
+++ b/proxyd/proxyd.go
@@ -55,6 +55,17 @@ func Start(config *Config) (func(), error) {
 		}
 	}
 
+	// While modifying shared globals is a bad practice, the alternative
+	// is to clone these errors on every invocation. This is inefficient.
+	// We'd also have to make sure that errors.Is and errors.As continue
+	// to function properly on the cloned errors.
+	if config.RateLimit.ErrorMessage != "" {
+		ErrOverRateLimit.Message = config.RateLimit.ErrorMessage
+	}
+	if config.WhitelistErrorMessage != "" {
+		ErrMethodNotWhitelisted.Message = config.WhitelistErrorMessage
+	}
+
 	maxConcurrentRPCs := config.Server.MaxConcurrentRPCs
 	if maxConcurrentRPCs == 0 {
 		maxConcurrentRPCs = math.MaxInt64
diff --git a/proxyd/server.go b/proxyd/server.go
index 455989dbd12b2..509dc6a338c5b 100644
--- a/proxyd/server.go
+++ b/proxyd/server.go
@@ -244,12 +244,7 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if isLimited("") {
-		rpcErr := ErrOverRateLimit
-		if s.limConfig.ErrorMessage != "" {
-			rpcErr = ErrOverRateLimit.Clone()
-			rpcErr.Message = s.limConfig.ErrorMessage
-		}
-		RecordRPCError(ctx, BackendProxyd, "unknown", rpcErr)
+		RecordRPCError(ctx, BackendProxyd, "unknown", ErrOverRateLimit)
 		log.Warn(
 			"rate limited request",
 			"req_id", GetReqID(ctx),
@@ -258,7 +253,7 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 			"origin", origin,
 			"remote_ip", xff,
 		)
-		writeRPCError(ctx, w, nil, rpcErr)
+		writeRPCError(ctx, w, nil, ErrOverRateLimit)
 		return
 	}
 
@@ -394,13 +389,8 @@ func (s *Server) handleBatchRPC(ctx context.Context, reqs []json.RawMessage, isL
 				"req_id", GetReqID(ctx),
 				"method", parsedReq.Method,
 			)
-			rpcErr := ErrOverRateLimit
-			if s.limConfig.ErrorMessage != "" {
-				rpcErr = rpcErr.Clone()
-				rpcErr.Message = s.limConfig.ErrorMessage
-			}
-			RecordRPCError(ctx, BackendProxyd, parsedReq.Method, rpcErr)
-			responses[i] = NewRPCErrorRes(parsedReq.ID, rpcErr)
+			RecordRPCError(ctx, BackendProxyd, parsedReq.Method, ErrOverRateLimit)
+			responses[i] = NewRPCErrorRes(parsedReq.ID, ErrOverRateLimit)
 			continue
 		}