diff --git a/SharpPhysFS/Interop.cs b/SharpPhysFS/Interop.cs
index da6328a..02d88cd 100644
--- a/SharpPhysFS/Interop.cs
+++ b/SharpPhysFS/Interop.cs
@@ -145,51 +145,54 @@ namespace SharpPhysFS
     [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
     public delegate void FnEnumerateFilesCallback(string s, EnumFilesCallback c, IntPtr ptr);
 
-    public static FnGetLinkedVersion PHYSFS_getLinkedVersion;
-    public static FnInit PHYSFS_init;
-    public static FnDeinit PHYSFS_deinit;
-    public static FnSupportedArchiveTypes PHYSFS_supportedArchiveTypes;
-    public static FnFreeList PHYSFS_freeList;
-    public static FnGetLastError PHYSFS_getLastError;
-    public static FnGetLastError PHYSFS_getDirSeparator;
-    public static FnPermitSymbolicLinks PHYSFS_permitSymbolicLinks;
-    public static FnSupportedArchiveTypes PHYSFS_getCdRomDirs;
-    public static FnGetLastError PHYSFS_getBaseDir;
-    public static FnGetLastError PHYSFS_getUserDir;
-    public static FnGetLastError PHYSFS_getWriteDir;
-    public static FnSetWriteDir PHYSFS_setWriteDir;
-    public static FnAddToSearchPath PHYSFS_addToSearchPath;
-    public static FnSetWriteDir PHYSFS_removeFromSearchPath;
-    public static FnSupportedArchiveTypes PHYSFS_getSearchPath;
-    public static FnSetSaneConfig PHYSFS_setSaneConfig;
-    public static FnSetWriteDir PHYSFS_mkdir;
-    public static FnSetWriteDir PHYSFS_delete;
-    public static FnEnumerateFiles PHYSFS_getRealDir;
-    public static FnEnumerateFiles PHYSFS_enumerateFiles;
-    public static FnSetWriteDir PHYSFS_exists;
-    public static FnSetWriteDir PHYSFS_isDirectory;
-    public static FnSetWriteDir PHYSFS_isSymbolicLink;
-    public static FnGetLastModTime PHYSFS_getLastModTime;
-    public static FnEnumerateFiles PHYSFS_openWrite;
-    public static FnEnumerateFiles PHYSFS_openAppend;
-    public static FnEnumerateFiles PHYSFS_openRead;
-    public static FnClose PHYSFS_close;
-    public static FnRead PHYSFS_read;
-    public static FnRead PHYSFS_write;
-    public static FnClose PHYSFS_eof;
-    public static FnTell PHYSFS_tell;
-    public static FnSeek PHYSFS_seek;
-    public static FnFileLength PHYSFS_fileLength;
-    public static FnSeek PHYSFS_setBuffer;
-    public static FnClose PHYSFS_flush;
-    public static FnDeinit PHYSFS_isInit;
-    public static FnDeinit PHYSFS_symbolicLinksPermitted;
-    public static FnSetAllocator PHYSFS_setAllocator;
-    public static FnMount PHYSFS_mount;
-    public static FnEnumerateFiles PHYSFS_getMountPoint;
-    public static FnGetCdRomDirsCallback PHYSFS_getCdRomDirsCallback;
-    public static FnGetCdRomDirsCallback PHYSFS_getSearchPathCallback;
-    public static FnEnumerateFilesCallback PHYSFS_enumerateFilesCallback;
+    // When the callbacks are not yet initialized, instead of throwing a
+    // null reference exception we explain the problem.
+    // I think it makes for a more graceful failure.
+    public static FnGetLinkedVersion PHYSFS_getLinkedVersion             = (ref Version v) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnInit PHYSFS_init                                     = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnDeinit PHYSFS_deinit                                 = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSupportedArchiveTypes PHYSFS_supportedArchiveTypes   = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnFreeList PHYSFS_freeList                             = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnGetLastError PHYSFS_getLastError                     = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnGetLastError PHYSFS_getDirSeparator                  = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnPermitSymbolicLinks PHYSFS_permitSymbolicLinks       = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSupportedArchiveTypes PHYSFS_getCdRomDirs            = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnGetLastError PHYSFS_getBaseDir                       = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnGetLastError PHYSFS_getUserDir                       = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnGetLastError PHYSFS_getWriteDir                      = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSetWriteDir PHYSFS_setWriteDir                       = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnAddToSearchPath PHYSFS_addToSearchPath               = (a, b) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSetWriteDir PHYSFS_removeFromSearchPath              = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSupportedArchiveTypes PHYSFS_getSearchPath           = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSetSaneConfig PHYSFS_setSaneConfig                   = (a, b, c, d, e) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSetWriteDir PHYSFS_mkdir                             = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSetWriteDir PHYSFS_delete                            = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnEnumerateFiles PHYSFS_getRealDir                     = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnEnumerateFiles PHYSFS_enumerateFiles                 = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSetWriteDir PHYSFS_exists                            = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSetWriteDir PHYSFS_isDirectory                       = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSetWriteDir PHYSFS_isSymbolicLink                    = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnGetLastModTime PHYSFS_getLastModTime                 = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnEnumerateFiles PHYSFS_openWrite                      = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnEnumerateFiles PHYSFS_openAppend                     = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnEnumerateFiles PHYSFS_openRead                       = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnClose PHYSFS_close                                   = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnRead PHYSFS_read                                     = (a, b, c, d) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnRead PHYSFS_write                                    = (a, b, c,d ) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnClose PHYSFS_eof                                     = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnTell PHYSFS_tell                                     = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSeek PHYSFS_seek                                     = (a, b) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnFileLength PHYSFS_fileLength                         = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSeek PHYSFS_setBuffer                                = (a, b) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnClose PHYSFS_flush                                   = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnDeinit PHYSFS_isInit                                 = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnDeinit PHYSFS_symbolicLinksPermitted                 = () => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnSetAllocator PHYSFS_setAllocator                     = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnMount PHYSFS_mount                                   = (a, b, c) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnEnumerateFiles PHYSFS_getMountPoint                  = (a) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnGetCdRomDirsCallback PHYSFS_getCdRomDirsCallback     = (a, b) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnGetCdRomDirsCallback PHYSFS_getSearchPathCallback    = (a, b) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
+    public static FnEnumerateFilesCallback PHYSFS_enumerateFilesCallback = (a, b, c) => { throw new InvalidOperationException("Callbacks not initialized yet"); };
 
     public static void SetUpInterop()
     {