diff --git a/PInvoke/Shell32/ShObjIdl.IKnownFolder.cs b/PInvoke/Shell32/ShObjIdl.IKnownFolder.cs
index 71108f2e..85e7832e 100644
--- a/PInvoke/Shell32/ShObjIdl.IKnownFolder.cs
+++ b/PInvoke/Shell32/ShObjIdl.IKnownFolder.cs
@@ -727,6 +727,22 @@ namespace Vanara.PInvoke
 			FOLDERID_Windows,
 		}
 
+		/// <summary>Frees the allocated fields in the result from IKnownFolder::GetFolderDefinition.</summary>
+		/// <param name="pKFD">
+		/// <para>Type: <c>KNOWNFOLDER_DEFINITION*</c></para>
+		/// <para>A pointer to a KNOWNFOLDER_DEFINITION structure that contains information about the given known folder.</para>
+		/// </param>
+		/// <returns>This function does not return a value.</returns>
+		/// <remarks>This is an inline helper function that calls CoTaskMemFree on the fields in the structure that need to be freed. Its implementation can be seen in the header file.</remarks>
+		// https://docs.microsoft.com/en-us/windows/desktop/api/shobjidl_core/nf-shobjidl_core-freeknownfolderdefinitionfields
+		// void FreeKnownFolderDefinitionFields( KNOWNFOLDER_DEFINITION *pKFD );
+		[PInvokeData("shobjidl_core.h", MSDNShortId = "0ad17dd3-e612-403a-b8c3-e93d5f259c1f")]
+		public static void FreeKnownFolderDefinitionFields(in KNOWNFOLDER_DEFINITION pKFD)
+		{
+			foreach (var fi in pKFD.GetType().GetFields().Where(f => f.FieldType == typeof(StrPtrUni)))
+				Marshal.FreeCoTaskMem((IntPtr)fi.GetValue(pKFD));
+		}
+
 		/// <summary>
 		/// Exposes methods that allow an application to retrieve information about a known folder's category, type, GUID, pointer to an item
 		/// identifier list (PIDL) value, redirection capabilities, and definition. It provides a method for the retrieval of a known folder's
@@ -975,13 +991,13 @@ namespace Vanara.PInvoke
 			/// settings. This name is meant to be a unique, human-readable name. Third parties are recommended to follow the format
 			/// Company.Application.Name. The name given here should not be confused with the display name.
 			/// </summary>
-			[MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(CoTaskMemStringMarshaler))] public string pszName;
+			public StrPtrUni pszName;
 
 			/// <summary>
 			/// A pointer to a short description of the known folder, stored as a null-terminated Unicode string. This description should
 			/// include the folder's purpose and usage.
 			/// </summary>
-			[MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(CoTaskMemStringMarshaler))] public string pszDescription;
+			public StrPtrUni pszDescription;
 
 			/// <summary>
 			/// A KNOWNFOLDERID value that names another known folder to serve as the parent folder. Applies to common and per-user folders
@@ -995,13 +1011,13 @@ namespace Vanara.PInvoke
 			/// refers to the physical file system path, and is not localized. Applies to common and per-user folders only. See Remarks for
 			/// more details.
 			/// </summary>
-			[MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(CoTaskMemStringMarshaler))] public string pszRelativePath;
+			public StrPtrUni pszRelativePath;
 
 			/// <summary>
 			/// A pointer to the Shell namespace folder path of the folder, stored as a null-terminated Unicode string. Applies to virtual
 			/// folders only. For example, Control Panel has a parsing name of ::%CLSID_MyComputer%\::%CLSID_ControlPanel%.
 			/// </summary>
-			[MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(CoTaskMemStringMarshaler))] public string pszParsingName;
+			public StrPtrUni pszParsingName;
 
 			/// <summary>
 			/// Optional. A pointer to the default tooltip resource used for this known folder when it is created. This is a null-terminated
@@ -1013,7 +1029,7 @@ namespace Vanara.PInvoke
 			/// </para>
 			/// <para>This information is not required for virtual folders.</para>
 			/// </summary>
-			[MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(CoTaskMemStringMarshaler))] public string pszTooltip;
+			public StrPtrUni pszTooltip;
 
 			/// <summary>
 			/// Optional. A pointer to the default localized name resource used when the folder is created. This is a null-terminated Unicode
@@ -1025,7 +1041,7 @@ namespace Vanara.PInvoke
 			/// </para>
 			/// <para>This information is not required for virtual folders.</para>
 			/// </summary>
-			[MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(CoTaskMemStringMarshaler))] public string pszLocalizedName;
+			public StrPtrUni pszLocalizedName;
 
 			/// <summary>
 			/// Optional. A pointer to the default icon resource used when the folder is created. This is a null-terminated Unicode string in
@@ -1037,7 +1053,7 @@ namespace Vanara.PInvoke
 			/// </para>
 			/// <para>This information is not required for virtual folders.</para>
 			/// </summary>
-			[MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(CoTaskMemStringMarshaler))] public string pszIcon;
+			public StrPtrUni pszIcon;
 
 			/// <summary>
 			/// Optional. A pointer to a Security Descriptor Definition Language format string. This is a null-terminated Unicode string that
@@ -1045,7 +1061,7 @@ namespace Vanara.PInvoke
 			/// folder inherits the security descriptor of its parent. This is particularly useful for common folders that are accessed by
 			/// all users.
 			/// </summary>
-			[MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(CoTaskMemStringMarshaler))] public string pszSecurity;
+			public StrPtrUni pszSecurity;
 
 			/// <summary>
 			/// Optional. Default file system attributes given to the folder when it is created. For example, the file could be hidden and
diff --git a/PInvoke/Shell32/ShTypes.cs b/PInvoke/Shell32/ShTypes.cs
index 88a545ed..fc97693c 100644
--- a/PInvoke/Shell32/ShTypes.cs
+++ b/PInvoke/Shell32/ShTypes.cs
@@ -134,27 +134,27 @@ namespace Vanara.PInvoke
 		public struct STRRET
 		{
 			/// <summary>A value that specifies the desired format of the string.</summary>
-			[FieldOffset(0)] public STRRET_TYPE uType;
+			[FieldOffset(0)]
+			public STRRET_TYPE uType;
 
 			/// <summary>
 			/// A pointer to the string. This memory must be allocated with CoTaskMemAlloc. It is the calling application's responsibility to
 			/// free this memory with CoTaskMemFree when it is no longer needed.
 			/// </summary>
-			[FieldOffset(4), MarshalAs(UnmanagedType.BStr)]
+			[FieldOffset(4)]
 			public StrPtrUni pOleStr; // must be freed by caller of GetDisplayNameOf
 
 			/// <summary>The offset into the item identifier list.</summary>
-			[FieldOffset(4)] public uint uOffset; // Offset into SHITEMID
+			[FieldOffset(4)]
+			public uint uOffset; // Offset into SHITEMID
 
 			/// <summary>The buffer to receive the display name. CHAR[MAX_PATH]</summary>
-			[FieldOffset(4), MarshalAs(UnmanagedType.LPStr, SizeConst = Kernel32.MAX_PATH)]
-			public string cStr; // Buffer to fill in (ANSI)
+			[FieldOffset(4)]
+			public StrPtrAnsi cStr;
 
 			/// <summary>Returns a <see cref="System.String"/> that represents this instance.</summary>
 			/// <returns>A <see cref="System.String"/> that represents this instance.</returns>
-			public override string ToString() => uType == STRRET_TYPE.STRRET_CSTR
-				? cStr
-				: (uType == STRRET_TYPE.STRRET_WSTR ? pOleStr.ToString() : string.Empty);
+			public override string ToString() => (uType == STRRET_TYPE.STRRET_CSTR ? cStr : (uType == STRRET_TYPE.STRRET_WSTR ? pOleStr : (string)null)) ?? string.Empty;
 		}
 
 		internal class STRRETMarshaler : ICustomMarshaler
diff --git a/PInvoke/Shell32/Thumbcache.cs b/PInvoke/Shell32/Thumbcache.cs
index 197e0898..87318991 100644
--- a/PInvoke/Shell32/Thumbcache.cs
+++ b/PInvoke/Shell32/Thumbcache.cs
@@ -53,7 +53,7 @@ namespace Vanara.PInvoke
 		/// </remarks>
 		// https://docs.microsoft.com/en-us/windows/desktop/api/thumbcache/nn-thumbcache-ithumbnailprovider
 		[PInvokeData("thumbcache.h", MSDNShortId = "55c4739a-4835-4f53-a435-804ddf06ffcf")]
-		[ComImport, Guid("e357fccd-a995-4576-b01f-234630154e96"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+		[ComImport, Guid("e357fccd-a995-4576-b01f-234630154e96"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown), CoClass(typeof(PhotoThumbnailProvider))]
 		public interface IThumbnailProvider
 		{
 			/// <summary>Gets a thumbnail image and alpha type.</summary>
@@ -79,26 +79,6 @@ namespace Vanara.PInvoke
 		/// <summary>An implementation of IThumbnailProvider for photo thumbnails is supplied in Microsoft Windows as CLSID_PhotoThumbnailProvider.</summary>
 		[ComImport, Guid("C7657C4A-9F68-40fa-A4DF-96BC08EB3551"), ClassInterface(ClassInterfaceType.None)]
 		[PInvokeData("thumbcache.h")]
-		public class PhotoThumbnailProvider : IThumbnailProvider
-		{
-			/// <summary>Gets a thumbnail image and alpha type.</summary>
-			/// <param name="cx">
-			/// The maximum thumbnail size, in pixels. The Shell draws the returned bitmap at this size or smaller. The returned bitmap
-			/// should fit into a square of width and height cx, though it does not need to be a square image. The Shell scales the bitmap to
-			/// render at lower sizes. For example, if the image has a 6:4 aspect ratio, then the returned bitmap should also have a 6:4
-			/// aspect ratio.
-			/// </param>
-			/// <param name="phbmp">
-			/// When this method returns, contains a pointer to the thumbnail image handle. The image must be a DIB section and 32 bits per
-			/// pixel. The Shell scales down the bitmap if its width or height is larger than the size specified by cx. The Shell always
-			/// respects the aspect ratio and never scales a bitmap larger than its original size.
-			/// </param>
-			/// <param name="pdwAlpha">
-			/// When this method returns, contains a pointer to one of the following values from the WTS_ALPHATYPE enumeration.
-			/// </param>
-			/// <returns>If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.</returns>
-			[PreserveSig]
-			public extern HRESULT GetThumbnail(uint cx, out HBITMAP phbmp, out WTS_ALPHATYPE pdwAlpha);
-		}
+		public class PhotoThumbnailProvider { }
 	}
 }
\ No newline at end of file