diff --git a/dlls/atl100/tests/atl.c b/dlls/atl100/tests/atl.c
index 4cf4a62ee01..383dbe45dce 100644
--- a/dlls/atl100/tests/atl.c
+++ b/dlls/atl100/tests/atl.c
@@ -43,21 +43,6 @@ static const GUID CATID_CatTest2 =
     {0x178fc163,0x0000,0x0000,{0x00,0x00,0x00,0x00,0x00,0x00,0x02,0x46}};
 #define CATID_CATTEST2_STR "178fc163-0000-0000-0000-000000000246"
 
-static const char *debugstr_guid(REFIID riid)
-{
-    static char buf[50];
-
-    if(!riid)
-        return "(null)";
-
-    sprintf(buf, "{%08x-%04x-%04x-%02x%02x-%02x%02x%02x%02x%02x%02x}",
-            riid->Data1, riid->Data2, riid->Data3, riid->Data4[0],
-            riid->Data4[1], riid->Data4[2], riid->Data4[3], riid->Data4[4],
-            riid->Data4[5], riid->Data4[6], riid->Data4[7]);
-
-    return buf;
-}
-
 static void test_winmodule(void)
 {
     _AtlCreateWndData create_data[3];
@@ -469,7 +454,7 @@ static HRESULT WINAPI Dispatch_QueryInterface(IDispatch *iface, REFIID riid, voi
         return S_OK;
     }
 
-    ok(0, "unexpected riid: %s\n", debugstr_guid(riid));
+    ok(0, "unexpected riid: %s\n", wine_dbgstr_guid(riid));
     return E_NOINTERFACE;
 }
 
@@ -548,8 +533,8 @@ static void test_source_iface(void)
     maj_ver = min_ver = 0xdead;
     hres = AtlGetObjectSourceInterface((IUnknown*)&Dispatch, &libid, &iid, &maj_ver, &min_ver);
     ok(hres == S_OK, "AtlGetObjectSourceInterface failed: %08x\n", hres);
-    ok(IsEqualGUID(&libid, &LIBID_MSHTML), "libid = %s\n", debugstr_guid(&libid));
-    ok(IsEqualGUID(&iid, &DIID_DispHTMLBody), "iid = %s\n", debugstr_guid(&iid));
+    ok(IsEqualGUID(&libid, &LIBID_MSHTML), "libid = %s\n", wine_dbgstr_guid(&libid));
+    ok(IsEqualGUID(&iid, &DIID_DispHTMLBody), "iid = %s\n", wine_dbgstr_guid(&iid));
     ok(maj_ver == 4 && min_ver == 0, "ver = %d.%d\n", maj_ver, min_ver);
 
     support_classinfo2 = FALSE;
@@ -558,8 +543,8 @@ static void test_source_iface(void)
     maj_ver = min_ver = 0xdead;
     hres = AtlGetObjectSourceInterface((IUnknown*)&Dispatch, &libid, &iid, &maj_ver, &min_ver);
     ok(hres == S_OK, "AtlGetObjectSourceInterface failed: %08x\n", hres);
-    ok(IsEqualGUID(&libid, &LIBID_MSHTML), "libid = %s\n", debugstr_guid(&libid));
-    ok(IsEqualGUID(&iid, &DIID_HTMLDocumentEvents), "iid = %s\n", debugstr_guid(&iid));
+    ok(IsEqualGUID(&libid, &LIBID_MSHTML), "libid = %s\n", wine_dbgstr_guid(&libid));
+    ok(IsEqualGUID(&iid, &DIID_HTMLDocumentEvents), "iid = %s\n", wine_dbgstr_guid(&iid));
     ok(maj_ver == 4 && min_ver == 0, "ver = %d.%d\n", maj_ver, min_ver);
 
     persist_clsid = CLSID_HTMLStyle;
@@ -567,8 +552,8 @@ static void test_source_iface(void)
     maj_ver = min_ver = 0xdead;
     hres = AtlGetObjectSourceInterface((IUnknown*)&Dispatch, &libid, &iid, &maj_ver, &min_ver);
     ok(hres == S_OK, "AtlGetObjectSourceInterface failed: %08x\n", hres);
-    ok(IsEqualGUID(&libid, &LIBID_MSHTML), "libid = %s\n", debugstr_guid(&libid));
-    ok(IsEqualGUID(&iid, &IID_NULL), "iid = %s\n", debugstr_guid(&iid));
+    ok(IsEqualGUID(&libid, &LIBID_MSHTML), "libid = %s\n", wine_dbgstr_guid(&libid));
+    ok(IsEqualGUID(&iid, &IID_NULL), "iid = %s\n", wine_dbgstr_guid(&iid));
     ok(maj_ver == 4 && min_ver == 0, "ver = %d.%d\n", maj_ver, min_ver);
 }