diff --git a/dlls/d3dx9_36/mesh.c b/dlls/d3dx9_36/mesh.c
index 844d521f8d1..166000fdb16 100644
--- a/dlls/d3dx9_36/mesh.c
+++ b/dlls/d3dx9_36/mesh.c
@@ -559,6 +559,8 @@ HRESULT WINAPI D3DXDeclaratorFromFVF(DWORD fvf, D3DVERTEXELEMENT9 declaration[MA
 
     TRACE("fvf %#x, declaration %p.\n", fvf, declaration);
 
+    if (fvf & (D3DFVF_RESERVED0 | D3DFVF_RESERVED2)) return D3DERR_INVALIDCALL;
+
     if (fvf & D3DFVF_POSITION_MASK)
     {
         BOOL has_blend = (fvf & D3DFVF_XYZB5) >= D3DFVF_XYZB1;
diff --git a/dlls/d3dx9_36/tests/mesh.c b/dlls/d3dx9_36/tests/mesh.c
index 05df51ec82f..c55a3c73f36 100644
--- a/dlls/d3dx9_36/tests/mesh.c
+++ b/dlls/d3dx9_36/tests/mesh.c
@@ -836,6 +836,8 @@ static void test_fvf_decl_conversion(void)
         };
         test_decl_to_fvf(decl, 0, D3DERR_INVALIDCALL, __LINE__, 0);
     }
+    /* Invalid FVFs cannot be converted to a declarator. */
+    test_fvf_to_decl(0xdeadbeef, NULL, D3DERR_INVALIDCALL, __LINE__, 0);
 }
 
 static void D3DXGetFVFVertexSizeTest(void)