diff --git a/dlls/wofutil/main.c b/dlls/wofutil/main.c
index 1866aed7c69..d8c891aa30c 100644
--- a/dlls/wofutil/main.c
+++ b/dlls/wofutil/main.c
@@ -23,6 +23,15 @@
 
 WINE_DEFAULT_DEBUG_CHANNEL(wofutil);
 
+HRESULT WINAPI WofIsExternalFile( const WCHAR *path, BOOL *result, ULONG *provider, void *ptr, ULONG *length )
+{
+    FIXME( "%s, %p, %p, %p, %p", debugstr_w(path), result, provider, ptr, length );
+    if (result) *result = FALSE;
+    if (provider) *provider = 0;
+    if (length) *length = 0;
+    return S_OK;
+}
+
 BOOL WINAPI WofShouldCompressBinaries( const WCHAR *volume, ULONG *alg )
 {
     FIXME( "%s, %p\n", debugstr_w(volume), alg );
diff --git a/dlls/wofutil/wofutil.spec b/dlls/wofutil/wofutil.spec
index 73f11c4f885..27a6ebd80eb 100644
--- a/dlls/wofutil/wofutil.spec
+++ b/dlls/wofutil/wofutil.spec
@@ -1,7 +1,7 @@
 @ stub WofEnumEntries
 @ stub WofFileEnumFiles
 @ stub WofGetDriverVersion
-@ stub WofIsExternalFile
+@ stdcall WofIsExternalFile(wstr ptr ptr ptr ptr)
 @ stub WofSetFileDataLocation
 @ stdcall WofShouldCompressBinaries(wstr ptr)
 @ stub WofWimAddEntry