diff --git a/Setup/Code.inc b/Setup/Code.inc
index 50bc4ed7c..3ddbe0958 100644
--- a/Setup/Code.inc
+++ b/Setup/Code.inc
@@ -131,6 +131,11 @@ begin
 		or RegKeyExists(HKLM,'SOFTWARE\Wow6432Node\Microsoft\VisualStudio\12.0\Projects\{FAE04EC0-301F-11d3-BF4B-00C04F79EFBC}');
 end;
 
+function PythonTools2013_Installed: Boolean;
+begin
+  Result := RegKeyExists(HKLM,'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\{7AD18985-A5E6-443D-B0AB-A9ECFBB389A0}');
+end;
+
 function Fsharp2013_Installed(dummy: string): Boolean;
 begin
   Result := RegKeyExists(HKLM,'SOFTWARE\Microsoft\VisualStudio\12.0\Projects\{f2a71f9b-5d33-465a-a702-920d77279786}')
diff --git a/Setup/Events.inc b/Setup/Events.inc
index 09a776218..630b24a4f 100644
--- a/Setup/Events.inc
+++ b/Setup/Events.inc
@@ -1,4 +1,77 @@
 [Code]
+/////////////////////////////////////////////////////////////////////
+function GetUninstallString(): String;
+var
+  sUnInstPath: String;
+  sUnInstallString: String;
+begin
+  sUnInstPath := ExpandConstant('Software\Microsoft\Windows\CurrentVersion\Uninstall\{#emit SetupSetting("AppId")}_is1');
+  sUnInstallString := '';
+  if not RegQueryStringValue(HKLM, sUnInstPath, 'UninstallString', sUnInstallString) then
+    RegQueryStringValue(HKCU, sUnInstPath, 'UninstallString', sUnInstallString);
+  Result := sUnInstallString;
+end;
+
+
+/////////////////////////////////////////////////////////////////////
+function IsUpgrade(): Boolean;
+begin
+  Result := (GetUninstallString() <> '');
+end;
+
+
+/////////////////////////////////////////////////////////////////////
+// Uninstall previously installed application.
+/////////////////////////////////////////////////////////////////////
+function UnInstallOldVersion(): Integer;
+var
+  sUnInstallString: String;
+  iResultCode: Integer;
+begin
+// Return Values:
+// 1 - uninstall string is empty
+// 2 - error executing the UnInstallString
+// 3 - successfully executed the UnInstallString
+
+  // default return value
+  Result := 0;
+
+  // get the uninstall string of the old app
+  sUnInstallString := GetUninstallString();
+  if sUnInstallString <> '' then begin
+    sUnInstallString := RemoveQuotes(sUnInstallString);
+    if Exec(sUnInstallString, '/SILENT /NORESTART /SUPPRESSMSGBOXES','', SW_HIDE, ewWaitUntilTerminated, iResultCode) then
+      Result := 3
+    else
+      Result := 2;
+  end else
+    Result := 1;
+end;
+
+/////////////////////////////////////////////////////////////////////
+// Uninstall previously installed application.
+/////////////////////////////////////////////////////////////////////
+procedure CleanupInterferringWithPyToolsGuid;
+begin
+  if not PythonTools2013_Installed then
+  begin
+    // Remove interferring registry string.
+    RegDeleteKeyIncludingSubkeys(HKLM, 'SOFTWARE\Wow6432Node\Microsoft\VisualStudio\12.0\CLSID\{8355452D-6D2F-41B0-89B8-BB2AA2529E94}')
+    RegDeleteKeyIncludingSubkeys(HKLM, 'Software\Microsoft\VisualStudio\12.0\CLSID\{8355452D-6D2F-41B0-89B8-BB2AA2529E94}');
+  end;
+end;
+
+/////////////////////////////////////////////////////////////////////
+procedure CurStepChanged(CurStep: TSetupStep);
+begin
+  if (CurStep=ssInstall) then
+  begin
+    if (IsUpgrade()) then
+    begin
+      CleanupInterferringWithPyToolsGuid();
+    end;
+  end;
+end;
 
 procedure CurUninstallStepChanged(CurUninstallStep: TUninstallStep);
 var