diff --git a/dlls/d3dx9_36/shader.c b/dlls/d3dx9_36/shader.c
index 5a0f1db77c6..bc5e002deba 100644
--- a/dlls/d3dx9_36/shader.c
+++ b/dlls/d3dx9_36/shader.c
@@ -1175,7 +1175,7 @@ HRESULT WINAPI D3DXGetShaderConstantTableEx(CONST DWORD* byte_code,
     if (hr != D3D_OK)
         return D3DXERR_INVALIDDATA;
 
-    object = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(ID3DXConstantTableImpl));
+    object = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(*object));
     if (!object)
     {
         ERR("Out of memory\n");