Index: src/gui/symbology-ng/qgsstylev2managerdialog.cpp
===================================================================
--- src/gui/symbology-ng/qgsstylev2managerdialog.cpp	(revision 15013)
+++ src/gui/symbology-ng/qgsstylev2managerdialog.cpp	(working copy)
@@ -13,6 +13,7 @@
 
 #include <QFile>
 #include <QInputDialog>
+#include <QMessageBox>
 #include <QStandardItemModel>
 
 #include "qgsapplication.h"
@@ -231,6 +232,20 @@
     return false;
   }
 
+  // check if there is no symbol with same name
+  if ( mStyle->symbolNames().contains( name ) )
+  {
+    int res = QMessageBox::warning( this, tr( "Save symbol" ),
+                                    tr( "Symbol with name '%1' already exists. Overwrite?" )
+                                    .arg( name ),
+                                    QMessageBox::Yes | QMessageBox::No );
+    if ( res != QMessageBox::Yes )
+    {
+      delete symbol;
+      return false;
+    }
+  }
+
   // add new symbol to style and re-populate the list
   mStyle->addSymbol( name, symbol );
   mModified = true;
Index: src/gui/symbology-ng/qgssymbolv2selectordialog.cpp
===================================================================
--- src/gui/symbology-ng/qgssymbolv2selectordialog.cpp	(revision 15013)
+++ src/gui/symbology-ng/qgssymbolv2selectordialog.cpp	(working copy)
@@ -14,6 +14,7 @@
 #include <QPainter>
 #include <QStandardItemModel>
 #include <QInputDialog>
+#include <QMessageBox>
 #include <QKeyEvent>
 #include <QMenu>
 
@@ -222,6 +223,19 @@
   if ( !ok || name.isEmpty() )
     return;
 
+  // check if there is no symbol with same name
+  if ( mStyle->symbolNames().contains( name ) )
+  {
+    int res = QMessageBox::warning( this, tr( "Save symbol" ),
+                                    tr( "Symbol with name '%1' already exists. Overwrite?" )
+                                    .arg( name ),
+                                    QMessageBox::Yes | QMessageBox::No );
+    if ( res != QMessageBox::Yes )
+    {
+      return;
+    }
+  }
+
   // add new symbol to style and re-populate the list
   mStyle->addSymbol( name, mSymbol->clone() );