diff --git a/src/main.go b/src/main.go
index 670dbbd..e114930 100644
--- a/src/main.go
+++ b/src/main.go
@@ -46,7 +46,6 @@ import (
 	"imuslab.com/zoraxy/mod/utils"
 )
 
-
 /* SIGTERM handler, do shutdown sequences before closing */
 func SetupCloseHandler() {
 	c := make(chan os.Signal, 2)
diff --git a/src/mod/geodb/geodb.go b/src/mod/geodb/geodb.go
index 6432b40..314a75e 100644
--- a/src/mod/geodb/geodb.go
+++ b/src/mod/geodb/geodb.go
@@ -3,6 +3,7 @@ package geodb
 import (
 	_ "embed"
 	"net/http"
+	"sync"
 	"time"
 
 	"imuslab.com/zoraxy/mod/database"
@@ -21,10 +22,10 @@ type Store struct {
 	geotrie                  *trie
 	geotrieIpv6              *trie
 	sysdb                    *database.Database
-	slowLookupCacheIpv4      map[string]string //Cache for slow lookup
-	slowLookupCacheIpv6      map[string]string //Cache for slow lookup
-	cacheClearTicker         *time.Ticker      //Ticker for clearing cache
-	cacheClearTickerStopChan chan bool         //Stop channel for cache clear ticker
+	slowLookupCacheIpv4      sync.Map     //Cache for slow lookup, ip -> cc
+	slowLookupCacheIpv6      sync.Map     //Cache for slow lookup ipv6, ip -> cc
+	cacheClearTicker         *time.Ticker //Ticker for clearing cache
+	cacheClearTickerStopChan chan bool    //Stop channel for cache clear ticker
 	option                   *StoreOptions
 }
 
@@ -61,7 +62,7 @@ func NewGeoDb(sysdb *database.Database, option *StoreOptions) (*Store, error) {
 	}
 
 	if option.SlowLookupCacheClearInterval == 0 {
-		option.SlowLookupCacheClearInterval = 15 * time.Minute
+		option.SlowLookupCacheClearInterval = 30 * time.Minute
 	}
 
 	//Create a new store
@@ -71,8 +72,8 @@ func NewGeoDb(sysdb *database.Database, option *StoreOptions) (*Store, error) {
 		geodbIpv6:                parsedGeoDataIpv6,
 		geotrieIpv6:              ipv6Trie,
 		sysdb:                    sysdb,
-		slowLookupCacheIpv4:      make(map[string]string),
-		slowLookupCacheIpv6:      make(map[string]string),
+		slowLookupCacheIpv4:      sync.Map{},
+		slowLookupCacheIpv6:      sync.Map{},
 		cacheClearTicker:         time.NewTicker(option.SlowLookupCacheClearInterval),
 		cacheClearTickerStopChan: make(chan bool),
 		option:                   option,
@@ -86,8 +87,8 @@ func NewGeoDb(sysdb *database.Database, option *StoreOptions) (*Store, error) {
 				case <-store.cacheClearTickerStopChan:
 					return
 				case <-thisGeoDBStore.cacheClearTicker.C:
-					thisGeoDBStore.slowLookupCacheIpv4 = make(map[string]string)
-					thisGeoDBStore.slowLookupCacheIpv6 = make(map[string]string)
+					thisGeoDBStore.slowLookupCacheIpv4 = sync.Map{}
+					thisGeoDBStore.slowLookupCacheIpv6 = sync.Map{}
 				}
 			}
 		}(thisGeoDBStore)
diff --git a/src/mod/geodb/geodb_test.go b/src/mod/geodb/geodb_test.go
index 4e3a784..d778e8a 100644
--- a/src/mod/geodb/geodb_test.go
+++ b/src/mod/geodb/geodb_test.go
@@ -42,7 +42,7 @@ func TestTrieConstruct(t *testing.T) {
 func TestResolveCountryCodeFromIP(t *testing.T) {
 	// Create a new store
 	store, err := geodb.NewGeoDb(nil, &geodb.StoreOptions{
-		false,
+		true,
 		true,
 		0,
 	})
@@ -84,4 +84,24 @@ func TestResolveCountryCodeFromIP(t *testing.T) {
 	if info.CountryIsoCode != expected {
 		t.Errorf("expected country code %s, but got %s for IP %s", expected, info.CountryIsoCode, ip)
 	}
+
+	// Test for issue #401
+	// Create 100 concurrent goroutines to resolve country code for random IP addresses in the test cases above
+	for i := 0; i < 100; i++ {
+		go func() {
+			for _, testcase := range knownIpCountryMap {
+				ip := testcase[0]
+				expected := testcase[1]
+				info, err := store.ResolveCountryCodeFromIP(ip)
+				if err != nil {
+					t.Errorf("error resolving country code for IP %s: %v", ip, err)
+					return
+				}
+				if info.CountryIsoCode != expected {
+					t.Errorf("expected country code %s, but got %s for IP %s", expected, info.CountryIsoCode, ip)
+				}
+			}
+		}()
+	}
+
 }
diff --git a/src/mod/geodb/slowSearch.go b/src/mod/geodb/slowSearch.go
index 8ebc977..8c79a4f 100644
--- a/src/mod/geodb/slowSearch.go
+++ b/src/mod/geodb/slowSearch.go
@@ -58,7 +58,8 @@ func (s *Store) slowSearchIpv4(ipAddr string) string {
 	}
 
 	//Check if already in cache
-	if cc, ok := s.slowLookupCacheIpv4[ipAddr]; ok {
+	cc := s.GetSlowSearchCachedIpv4(ipAddr)
+	if cc != "" {
 		return cc
 	}
 
@@ -70,7 +71,7 @@ func (s *Store) slowSearchIpv4(ipAddr string) string {
 		inRange, _ := isIPv4InRange(startIp, endIp, ipAddr)
 		if inRange {
 			//Add to cache
-			s.slowLookupCacheIpv4[ipAddr] = cc
+			s.slowLookupCacheIpv4.Store(ipAddr, cc)
 			return cc
 		}
 	}
@@ -83,7 +84,8 @@ func (s *Store) slowSearchIpv6(ipAddr string) string {
 	}
 
 	//Check if already in cache
-	if cc, ok := s.slowLookupCacheIpv6[ipAddr]; ok {
+	cc := s.GetSlowSearchCachedIpv6(ipAddr)
+	if cc != "" {
 		return cc
 	}
 
@@ -95,9 +97,27 @@ func (s *Store) slowSearchIpv6(ipAddr string) string {
 		inRange, _ := isIPv6InRange(startIp, endIp, ipAddr)
 		if inRange {
 			//Add to cache
-			s.slowLookupCacheIpv6[ipAddr] = cc
+			s.slowLookupCacheIpv6.Store(ipAddr, cc)
 			return cc
 		}
 	}
 	return ""
 }
+
+// GetSlowSearchCachedIpv4 return the country code for the given ipv4 address, return empty string if not found
+func (s *Store) GetSlowSearchCachedIpv4(ipAddr string) string {
+	cc, ok := s.slowLookupCacheIpv4.Load(ipAddr)
+	if ok {
+		return cc.(string)
+	}
+	return ""
+}
+
+// GetSlowSearchCachedIpv6 return the country code for the given ipv6 address, return empty string if not found
+func (s *Store) GetSlowSearchCachedIpv6(ipAddr string) string {
+	cc, ok := s.slowLookupCacheIpv6.Load(ipAddr)
+	if ok {
+		return cc.(string)
+	}
+	return ""
+}