diff --git a/lib/KOReaderSync/KOReaderCredentialStore.cpp b/lib/KOReaderSync/KOReaderCredentialStore.cpp
index b9cbc564..6eb37ac8 100644
--- a/lib/KOReaderSync/KOReaderCredentialStore.cpp
+++ b/lib/KOReaderSync/KOReaderCredentialStore.cpp
@@ -15,6 +15,9 @@ constexpr uint8_t KOREADER_FILE_VERSION = 1;
 // KOReader credentials file path
 constexpr char KOREADER_FILE[] = "/.crosspoint/koreader.bin";
 
+// Default sync server URL
+constexpr char DEFAULT_SERVER_URL[] = "https://sync.koreader.rocks:443";
+
 // Obfuscation key - "KOReader" in ASCII
 // This is NOT cryptographic security, just prevents casual file reading
 constexpr uint8_t OBFUSCATION_KEY[] = {0x4B, 0x4F, 0x52, 0x65, 0x61, 0x64, 0x65, 0x72};
@@ -48,6 +51,9 @@ bool KOReaderCredentialStore::saveToFile() const {
   obfuscate(obfuscatedPwd);
   serialization::writeString(file, obfuscatedPwd);
 
+  // Write server URL
+  serialization::writeString(file, serverUrl);
+
   file.close();
   Serial.printf("[%lu] [KRS] Saved KOReader credentials to file\n", millis());
   return true;
@@ -70,11 +76,26 @@ bool KOReaderCredentialStore::loadFromFile() {
   }
 
   // Read username
-  serialization::readString(file, username);
+  if (file.available()) {
+    serialization::readString(file, username);
+  } else {
+    username.clear();
+  }
 
   // Read and deobfuscate password
-  serialization::readString(file, password);
-  obfuscate(password);  // XOR is symmetric, so same function deobfuscates
+  if (file.available()) {
+    serialization::readString(file, password);
+    obfuscate(password);  // XOR is symmetric, so same function deobfuscates
+  } else {
+    password.clear();
+  }
+
+  // Read server URL
+  if (file.available()) {
+    serialization::readString(file, serverUrl);
+  } else {
+    serverUrl.clear();
+  }
 
   file.close();
   Serial.printf("[%lu] [KRS] Loaded KOReader credentials for user: %s\n", millis(), username.c_str());
@@ -109,3 +130,21 @@ void KOReaderCredentialStore::clearCredentials() {
   saveToFile();
   Serial.printf("[%lu] [KRS] Cleared KOReader credentials\n", millis());
 }
+
+void KOReaderCredentialStore::setServerUrl(const std::string& url) {
+  serverUrl = url;
+  Serial.printf("[%lu] [KRS] Set server URL: %s\n", millis(), url.empty() ? "(default)" : url.c_str());
+}
+
+std::string KOReaderCredentialStore::getBaseUrl() const {
+  if (serverUrl.empty()) {
+    return DEFAULT_SERVER_URL;
+  }
+
+  // Normalize URL: add https:// if no protocol specified
+  if (serverUrl.find("://") == std::string::npos) {
+    return "https://" + serverUrl;
+  }
+
+  return serverUrl;
+}
diff --git a/lib/KOReaderSync/KOReaderCredentialStore.h b/lib/KOReaderSync/KOReaderCredentialStore.h
index 0d3332fa..488f23b0 100644
--- a/lib/KOReaderSync/KOReaderCredentialStore.h
+++ b/lib/KOReaderSync/KOReaderCredentialStore.h
@@ -11,6 +11,7 @@ class KOReaderCredentialStore {
   static KOReaderCredentialStore instance;
   std::string username;
   std::string password;
+  std::string serverUrl;  // Custom sync server URL (empty = default)
 
   // Private constructor for singleton
   KOReaderCredentialStore() = default;
@@ -43,6 +44,13 @@ class KOReaderCredentialStore {
 
   // Clear credentials
   void clearCredentials();
+
+  // Server URL management
+  void setServerUrl(const std::string& url);
+  const std::string& getServerUrl() const { return serverUrl; }
+
+  // Get base URL for API calls (with https:// normalization, falls back to default)
+  std::string getBaseUrl() const;
 };
 
 // Helper macro to access credential store
diff --git a/lib/KOReaderSync/KOReaderSyncClient.cpp b/lib/KOReaderSync/KOReaderSyncClient.cpp
index 8fa7fc34..91515cd9 100644
--- a/lib/KOReaderSync/KOReaderSyncClient.cpp
+++ b/lib/KOReaderSync/KOReaderSyncClient.cpp
@@ -10,9 +10,6 @@
 #include "KOReaderCredentialStore.h"
 
 namespace {
-// Base URL for KOReader sync server
-constexpr char BASE_URL[] = "https://sync.koreader.rocks:443";
-
 // Device identifier for CrossPoint reader
 constexpr char DEVICE_NAME[] = "CrossPoint";
 constexpr char DEVICE_ID[] = "crosspoint-reader";
@@ -34,7 +31,7 @@ KOReaderSyncClient::Error KOReaderSyncClient::authenticate() {
   client->setInsecure();
   HTTPClient http;
 
-  std::string url = std::string(BASE_URL) + "/users/auth";
+  std::string url = KOREADER_STORE.getBaseUrl() + "/users/auth";
   Serial.printf("[%lu] [KOSync] Authenticating: %s\n", millis(), url.c_str());
 
   http.begin(*client, url.c_str());
@@ -66,7 +63,7 @@ KOReaderSyncClient::Error KOReaderSyncClient::getProgress(const std::string& doc
   client->setInsecure();
   HTTPClient http;
 
-  std::string url = std::string(BASE_URL) + "/syncs/progress/" + documentHash;
+  std::string url = KOREADER_STORE.getBaseUrl() + "/syncs/progress/" + documentHash;
   Serial.printf("[%lu] [KOSync] Getting progress: %s\n", millis(), url.c_str());
 
   http.begin(*client, url.c_str());
@@ -121,7 +118,7 @@ KOReaderSyncClient::Error KOReaderSyncClient::updateProgress(const KOReaderProgr
   client->setInsecure();
   HTTPClient http;
 
-  std::string url = std::string(BASE_URL) + "/syncs/progress";
+  std::string url = KOREADER_STORE.getBaseUrl() + "/syncs/progress";
   Serial.printf("[%lu] [KOSync] Updating progress: %s\n", millis(), url.c_str());
 
   http.begin(*client, url.c_str());
diff --git a/src/activities/settings/KOReaderSettingsActivity.cpp b/src/activities/settings/KOReaderSettingsActivity.cpp
index 9a6c0f98..4b16e966 100644
--- a/src/activities/settings/KOReaderSettingsActivity.cpp
+++ b/src/activities/settings/KOReaderSettingsActivity.cpp
@@ -11,8 +11,8 @@
 #include "fontIds.h"
 
 namespace {
-constexpr int MENU_ITEMS = 3;
-const char* menuNames[MENU_ITEMS] = {"Username", "Password", "Authenticate"};
+constexpr int MENU_ITEMS = 4;
+const char* menuNames[MENU_ITEMS] = {"Username", "Password", "Sync Server URL", "Authenticate"};
 }  // namespace
 
 void KOReaderSettingsActivity::taskTrampoline(void* param) {
@@ -112,6 +112,23 @@ void KOReaderSettingsActivity::handleSelection() {
           updateRequired = true;
         }));
   } else if (selectedIndex == 2) {
+    // Sync Server URL
+    exitActivity();
+    enterNewActivity(new KeyboardEntryActivity(
+        renderer, mappedInput, "Sync Server URL", KOREADER_STORE.getServerUrl(), 10,
+        128,    // maxLength - URLs can be long
+        false,  // not password
+        [this](const std::string& url) {
+          KOREADER_STORE.setServerUrl(url);
+          KOREADER_STORE.saveToFile();
+          exitActivity();
+          updateRequired = true;
+        },
+        [this]() {
+          exitActivity();
+          updateRequired = true;
+        }));
+  } else if (selectedIndex == 3) {
     // Authenticate
     if (!KOREADER_STORE.hasCredentials()) {
       // Can't authenticate without credentials - just show message briefly
@@ -158,13 +175,15 @@ void KOReaderSettingsActivity::render() {
 
     renderer.drawText(UI_10_FONT_ID, 20, settingY, menuNames[i], !isSelected);
 
-    // Draw status for username/password
+    // Draw status for each item
     const char* status = "";
     if (i == 0) {
       status = KOREADER_STORE.getUsername().empty() ? "[Not Set]" : "[Set]";
     } else if (i == 1) {
       status = KOREADER_STORE.getPassword().empty() ? "[Not Set]" : "[Set]";
     } else if (i == 2) {
+      status = KOREADER_STORE.getServerUrl().empty() ? "[Not Set]" : "[Set]";
+    } else if (i == 3) {
       status = KOREADER_STORE.hasCredentials() ? "" : "[Set credentials first]";
     }