Also add the other case, to prevent accidental change to public

src/devices/Common/ClassVisibility.cs

@@ -7,12 +7,12 @@
 using System.Text;
 using System.Threading.Tasks;
 
+#pragma warning disable SA1403 // File may only contain a single namespace
+
 // These instructions make the classes public for building the individual projects.
 // The default visibility is "internal" so they stay hidden if this section is removed for the final library build.
 #if !BUILDING_IOT_DEVICE_BINDINGS
 
-#pragma warning disable SA1403 // File may only contain a single namespace
-
 public partial class Interop
 {
 }
@@ -42,5 +42,36 @@ public partial struct PinVector64
     }
 }
 
+#else
+
+internal partial class Interop
+{
+}
+
+namespace Iot.Device.Common
+{
+    internal partial class NumberHelper
+    {
+    }
+}
+
+namespace System.Device
+{
+    internal partial class DelayHelper
+    {
+    }
+}
+
+namespace System.Device.Gpio
+{
+    internal partial struct PinVector32
+    {
+    }
+
+    internal partial struct PinVector64
+    {
+    }
+}
+
 
 #endif