diff --git a/build.cake b/build.cake
index 45f2d9e18d..4e18f23780 100644
--- a/build.cake
+++ b/build.cake
@@ -6,7 +6,7 @@
 #addin "nuget:?package=NuGet.Core&version=2.12.0"
 #tool "nuget:?package=xunit.runner.console&version=2.2.0"
 #tool "nuget:https://dotnet.myget.org/F/nuget-build/?package=NuGet.CommandLine&version=4.3.0-preview1-3980&prerelease"
-#tool "JetBrains.ReSharper.CommandLineTools"
+#tool "nuget:?package=JetBrains.ReSharper.CommandLineTools&version=2017.1.20170613.162720"
 ///////////////////////////////////////////////////////////////////////////////
 // TOOLS
 ///////////////////////////////////////////////////////////////////////////////
diff --git a/src/Gtk/Avalonia.Gtk3/Interop/Utf8Buffer.cs b/src/Gtk/Avalonia.Gtk3/Interop/Utf8Buffer.cs
index fc76fefd1a..c932aac950 100644
--- a/src/Gtk/Avalonia.Gtk3/Interop/Utf8Buffer.cs
+++ b/src/Gtk/Avalonia.Gtk3/Interop/Utf8Buffer.cs
@@ -36,6 +36,8 @@ namespace Avalonia.Gtk3.Interop
         public static unsafe string StringFromPtr(IntPtr s)
         {
             var pstr = (byte*)s;
+            if (pstr == null)
+                return null;
             int len;
             for (len = 0; pstr[len] != 0; len++) ;
             var bytes = new byte[len];