diff --git a/src/dpiConn.c b/src/dpiConn.c
index 82aea31e..67b6a8ef 100644
--- a/src/dpiConn.c
+++ b/src/dpiConn.c
@@ -2147,6 +2147,7 @@ int dpiConn_subscribe(dpiConn *conn, dpiSubscrCreateParams *params,
 int dpiConn_unsubscribe(dpiConn *conn, dpiSubscr *subscr)
 {
     dpiError error;
+    int status;
 
     if (dpiConn__check(conn, __func__, &error) < 0)
         return dpiGen__endPublicFn(conn, DPI_FAILURE, &error);
@@ -2154,9 +2155,13 @@ int dpiConn_unsubscribe(dpiConn *conn, dpiSubscr *subscr)
             &error) < 0)
         return dpiGen__endPublicFn(conn, DPI_FAILURE, &error);
     if (subscr->registered) {
-        if (dpiOci__subscriptionUnRegister(conn, subscr, &error) < 0)
+        dpiMutex__acquire(subscr->mutex);
+        status = dpiOci__subscriptionUnRegister(conn, subscr, &error);
+        if (status == DPI_SUCCESS)
+            subscr->registered = 0;
+        dpiMutex__release(subscr->mutex);
+        if (status < 0)
             return dpiGen__endPublicFn(subscr, DPI_FAILURE, &error);
-        subscr->registered = 0;
     }
 
     dpiGen__setRefCount(subscr, &error, -1);
diff --git a/src/dpiImpl.h b/src/dpiImpl.h
index d0db476b..e008e09a 100644
--- a/src/dpiImpl.h
+++ b/src/dpiImpl.h
@@ -1047,6 +1047,7 @@ struct dpiSubscr {
     dpiType_HEAD
     dpiConn *conn;                      // connection which created this
     void *handle;                       // OCI subscription handle
+    dpiMutexType mutex;                 // enables thread safety
     dpiSubscrNamespace subscrNamespace; // OCI namespace
     dpiSubscrQOS qos;                   // quality of service flags
     dpiSubscrCallback callback;         // callback when event is propagated
diff --git a/src/dpiSubscr.c b/src/dpiSubscr.c
index d0750c59..c4b00a55 100644
--- a/src/dpiSubscr.c
+++ b/src/dpiSubscr.c
@@ -41,8 +41,18 @@ static void dpiSubscr__callback(dpiSubscr *subscr, UNUSED void *handle,
 
     // ensure that the subscription handle is still valid
     if (dpiGen__startPublicFn(subscr, DPI_HTYPE_SUBSCR, __func__, 1,
-            &error) < 0)
+            &error) < 0) {
         dpiGen__endPublicFn(subscr, DPI_FAILURE, &error);
+        return;
+    }
+
+    // if the subscription is no longer registered, nothing further to do
+    dpiMutex__acquire(subscr->mutex);
+    if (!subscr->registered) {
+        dpiMutex__release(subscr->mutex);
+        dpiGen__endPublicFn(subscr, DPI_SUCCESS, &error);
+        return;
+    }
 
     // populate message
     memset(&message, 0, sizeof(message));
@@ -52,11 +62,13 @@ static void dpiSubscr__callback(dpiSubscr *subscr, UNUSED void *handle,
     }
     message.registered = subscr->registered;
 
-    // invoke user callback
+    // invoke user callback; temporarily increase reference count to ensure
+    // that the subscription is not freed during the callback
+    dpiGen__setRefCount(subscr, &error, 1);
     (*subscr->callback)(subscr->callbackContext, &message);
-
-    // clean up message
     dpiSubscr__freeMessage(&message);
+    dpiMutex__release(subscr->mutex);
+    dpiGen__setRefCount(subscr, &error, -1);
     dpiGen__endPublicFn(subscr, DPI_SUCCESS, &error);
 }
 
@@ -95,6 +107,7 @@ int dpiSubscr__create(dpiSubscr *subscr, dpiConn *conn,
     subscr->callbackContext = params->callbackContext;
     subscr->subscrNamespace = params->subscrNamespace;
     subscr->qos = params->qos;
+    dpiMutex__initialize(subscr->mutex);
 
     // create the subscription handle
     if (dpiOci__handleAlloc(conn->env->handle, &subscr->handle,
@@ -237,6 +250,7 @@ int dpiSubscr__create(dpiSubscr *subscr, dpiConn *conn,
 //-----------------------------------------------------------------------------
 void dpiSubscr__free(dpiSubscr *subscr, dpiError *error)
 {
+    dpiMutex__acquire(subscr->mutex);
     if (subscr->handle) {
         if (subscr->registered)
             dpiOci__subscriptionUnRegister(subscr->conn, subscr, error);
@@ -247,6 +261,8 @@ void dpiSubscr__free(dpiSubscr *subscr, dpiError *error)
         dpiGen__setRefCount(subscr->conn, error, -1);
         subscr->conn = NULL;
     }
+    dpiMutex__release(subscr->mutex);
+    dpiMutex__destroy(subscr->mutex);
     dpiUtils__freeMemory(subscr);
 }