diff --git a/include/dxfeed_graal_cpp_api/api/DXFeedSubscription.hpp b/include/dxfeed_graal_cpp_api/api/DXFeedSubscription.hpp
index af56ba90..ce0e9994 100644
--- a/include/dxfeed_graal_cpp_api/api/DXFeedSubscription.hpp
+++ b/include/dxfeed_graal_cpp_api/api/DXFeedSubscription.hpp
@@ -272,14 +272,7 @@ class DXFCPP_EXPORT DXFeedSubscription : public RequireMakeShared<DXFeedSubscrip
      * event listeners and subscription change listeners and makes sure that no more listeners
      * can be added.
      */
-    void close() const {
-        if constexpr (Debugger::isDebug) {
-            // ReSharper disable once CppDFAUnreachableCode
-            Debugger::debug(toString() + "::close()");
-        }
-
-        closeImpl();
-    }
+    void close() const;
 
     /**
      * Adds listener for events.
diff --git a/include/dxfeed_graal_cpp_api/isolated/api/IsolatedDXFeedSubscription.hpp b/include/dxfeed_graal_cpp_api/isolated/api/IsolatedDXFeedSubscription.hpp
index b55c7662..45bd494f 100644
--- a/include/dxfeed_graal_cpp_api/isolated/api/IsolatedDXFeedSubscription.hpp
+++ b/include/dxfeed_graal_cpp_api/isolated/api/IsolatedDXFeedSubscription.hpp
@@ -17,9 +17,6 @@ namespace isolated::api::IsolatedDXFeedSubscription {
 
 /*
 
-int32_t                   dxfg_DXFeedSubscription_addEventListener(graal_isolatethread_t *thread, dxfg_subscription_t
-*sub, dxfg_feed_event_listener_t *listener);
-
 int32_t                   dxfg_DXFeedSubscription_removeEventListener(graal_isolatethread_t *thread, dxfg_subscription_t
 *sub, dxfg_feed_event_listener_t *listener);
 
@@ -113,6 +110,21 @@ void /* int32_t */
 addEventListener(/* dxfg_subscription_t * */ const JavaObjectHandle<DXFeedSubscription> &sub,
                  /* dxfg_feed_event_listener_t * */ const JavaObjectHandle<DXFeedEventListener> &listener);
 
+// int32_t dxfg_DXFeedSubscription_removeEventListener(graal_isolatethread_t *thread, dxfg_subscription_t *sub, dxfg_feed_event_listener_t *listener);
+
+// int32_t dxfg_DXFeedSubscription_addSymbol(graal_isolatethread_t *thread, dxfg_subscription_t *sub, dxfg_symbol_t *symbol);
+
+/**
+ * Calls the Graal SDK function `dxfg_DXFeedSubscription_addSymbol` in isolation.
+ *
+ * @param sub The subscription's handle.
+ * @param symbol The symbol.
+ * @throws std::invalid_argument if DXFeedSubscription's handle is invalid or the symbol is nullptr.
+ * @throws JavaException if something happened with the dxFeed API backend.
+ * @throws GraalException if something happened with the GraalVM.
+ */
+void /* int32_t */ addSymbol(/* dxfg_subscription_t * */ const JavaObjectHandle<DXFeedSubscription> &sub, /* dxfg_symbol_t * */ void* symbol);
+
 /**
  * Calls the Graal SDK function `dxfg_DXFeedSubscription_addChangeListener` in isolation.
  *
diff --git a/src/api/DXFeedSubscription.cpp b/src/api/DXFeedSubscription.cpp
index 05072525..e6b62633 100644
--- a/src/api/DXFeedSubscription.cpp
+++ b/src/api/DXFeedSubscription.cpp
@@ -25,7 +25,7 @@ struct DXFeedSubscription::Impl {
 
             sub->onEvent_(events);
         }
-    };
+    }
 };
 
 void DXFeedSubscription::attach(std::shared_ptr<DXFeed> feed) {
@@ -44,6 +44,15 @@ void DXFeedSubscription::detach(std::shared_ptr<DXFeed> feed) {
     feed->detachSubscription(sharedAs<DXFeedSubscription>());
 }
 
+void DXFeedSubscription::close() const {
+    if constexpr (Debugger::isDebug) {
+        // ReSharper disable once CppDFAUnreachableCode
+        Debugger::debug(toString() + "::close()");
+    }
+
+    closeImpl();
+}
+
 std::size_t DXFeedSubscription::addChangeListener(std::shared_ptr<ObservableSubscriptionChangeListener> listener) {
     isolated::api::IsolatedDXFeedSubscription::addChangeListener(handle_, listener->getHandle());
 
@@ -77,16 +86,7 @@ void DXFeedSubscription::removeChangeListener(std::size_t changeListenerId) {
 }
 
 void DXFeedSubscription::addSymbolImpl(void *graalSymbol) const {
-    if (!handle_) {
-        return;
-    }
-
-    runIsolatedOrElse(
-        [handle = static_cast<dxfg_subscription_t *>(handle_.get()), graalSymbol](auto threadHandle) {
-            return dxfg_DXFeedSubscription_addSymbol(static_cast<graal_isolatethread_t *>(threadHandle), handle,
-                                                     static_cast<dxfg_symbol_t *>(graalSymbol)) == 0;
-        },
-        false);
+    isolated::api::IsolatedDXFeedSubscription::addSymbol(handle_, graalSymbol);
 }
 
 void DXFeedSubscription::addSymbolsImpl(void *graalSymbolList) const {
diff --git a/src/isolated/api/IsolatedDXFeedSubscription.cpp b/src/isolated/api/IsolatedDXFeedSubscription.cpp
index aeb9b845..f4d37317 100644
--- a/src/isolated/api/IsolatedDXFeedSubscription.cpp
+++ b/src/isolated/api/IsolatedDXFeedSubscription.cpp
@@ -54,6 +54,23 @@ addEventListener(/* dxfg_subscription_t * */ const JavaObjectHandle<DXFeedSubscr
                                            static_cast<dxfg_feed_event_listener_t *>(listener.get()));
 }
 
+void /* int32_t */ addSymbol(/* dxfg_subscription_t * */ const JavaObjectHandle<DXFeedSubscription> &sub,
+                             /* dxfg_symbol_t * */ void *symbol) {
+    if (!sub) {
+        throw std::invalid_argument(
+            "Unable to execute function `dxfg_DXFeedSubscription_addSymbol`. The `sub` handle is invalid");
+    }
+
+    if (!symbol) {
+        throw std::invalid_argument("Unable to execute function `dxfg_DXFeedSubscription_addSymbol`. The "
+                                    "`symbol` is nullptr");
+    }
+
+    runGraalFunctionAndThrowIfLessThanZero(dxfg_DXFeedSubscription_addSymbol,
+                                           static_cast<dxfg_subscription_t *>(sub.get()),
+                                           static_cast<dxfg_symbol_t *>(symbol));
+}
+
 void /* int32_t */ addChangeListener(
     /* dxfg_subscription_t * */ const JavaObjectHandle<DXFeedSubscription> &sub,
     /* dxfg_observable_subscription_change_listener_t * */ const JavaObjectHandle<ObservableSubscriptionChangeListener>