diff --git a/dlls/oledb32/datainit.c b/dlls/oledb32/datainit.c
index 3694ac67fec..c2066712f8b 100644
--- a/dlls/oledb32/datainit.c
+++ b/dlls/oledb32/datainit.c
@@ -631,7 +631,7 @@ static WCHAR *strstriW(const WCHAR *str, const WCHAR *sub)
     return r;
 }
 
-HRESULT get_data_source(IUnknown *outer, DWORD clsctx, LPWSTR initstring, REFIID riid, IUnknown **datasource)
+HRESULT get_data_source(IUnknown *outer, DWORD clsctx, LPCOLESTR initstring, REFIID riid, IUnknown **datasource)
 {
     static const WCHAR providerW[] = L"Provider=";
     BOOL datasource_created = FALSE;
@@ -768,7 +768,7 @@ HRESULT get_data_source(IUnknown *outer, DWORD clsctx, LPWSTR initstring, REFIID
 }
 
 static HRESULT WINAPI datainit_GetDataSource(IDataInitialize *iface, IUnknown *outer, DWORD clsctx,
-                                LPWSTR initstring, REFIID riid, IUnknown **datasource)
+                                LPCOLESTR initstring, REFIID riid, IUnknown **datasource)
 {
     datainit *This = impl_from_IDataInitialize(iface);
 
@@ -977,7 +977,7 @@ static HRESULT WINAPI datainit_CreateDBInstanceEx(IDataInitialize *iface, REFCLS
     return E_NOTIMPL;
 }
 
-static HRESULT WINAPI datainit_LoadStringFromStorage(IDataInitialize *iface, LPWSTR pwszFileName,
+static HRESULT WINAPI datainit_LoadStringFromStorage(IDataInitialize *iface, LPCOLESTR pwszFileName,
                                 LPWSTR *ppwszInitializationString)
 {
     datainit *This = impl_from_IDataInitialize(iface);
@@ -987,8 +987,8 @@ static HRESULT WINAPI datainit_LoadStringFromStorage(IDataInitialize *iface, LPW
     return E_NOTIMPL;
 }
 
-static HRESULT WINAPI datainit_WriteStringToStorage(IDataInitialize *iface, LPWSTR pwszFileName,
-                                LPWSTR pwszInitializationString, DWORD dwCreationDisposition)
+static HRESULT WINAPI datainit_WriteStringToStorage(IDataInitialize *iface, LPCOLESTR pwszFileName,
+                                LPCOLESTR pwszInitializationString, DWORD dwCreationDisposition)
 {
     datainit *This = impl_from_IDataInitialize(iface);
 
diff --git a/dlls/oledb32/dslocator.c b/dlls/oledb32/dslocator.c
index 6991be65f65..066f14a5508 100644
--- a/dlls/oledb32/dslocator.c
+++ b/dlls/oledb32/dslocator.c
@@ -707,7 +707,7 @@ static ULONG WINAPI datainitialize_Release(IDataInitialize *iface)
 }
 
 static HRESULT WINAPI datainitialize_GetDataSource(IDataInitialize *iface,
-    IUnknown *outer, DWORD context, LPWSTR initstring, REFIID riid, IUnknown **datasource)
+    IUnknown *outer, DWORD context, LPCOLESTR initstring, REFIID riid, IUnknown **datasource)
 {
     TRACE("(%p)->(%p %#lx %s %s %p)\n", iface, outer, context, debugstr_w(initstring), debugstr_guid(riid),
         datasource);
@@ -738,13 +738,13 @@ static HRESULT WINAPI datainitialize_CreateDBInstanceEx(IDataInitialize *iface,
     return E_NOTIMPL;
 }
 
-static HRESULT WINAPI datainitialize_LoadStringFromStorage(IDataInitialize *iface, LPWSTR filename, LPWSTR *initstring)
+static HRESULT WINAPI datainitialize_LoadStringFromStorage(IDataInitialize *iface, LPCOLESTR filename, LPWSTR *initstring)
 {
     FIXME("(%p)->(%s %p): stub\n", iface, debugstr_w(filename), initstring);
     return E_NOTIMPL;
 }
 
-static HRESULT WINAPI datainitialize_WriteStringToStorage(IDataInitialize *iface, LPWSTR filename, LPWSTR initstring,
+static HRESULT WINAPI datainitialize_WriteStringToStorage(IDataInitialize *iface, LPCOLESTR filename, LPCOLESTR initstring,
     DWORD disposition)
 {
     FIXME("(%p)->(%s %s %#lx): stub\n", iface, debugstr_w(filename), debugstr_w(initstring), disposition);
diff --git a/dlls/oledb32/oledb_private.h b/dlls/oledb32/oledb_private.h
index 3bc16f73f52..278b3c47f0e 100644
--- a/dlls/oledb32/oledb_private.h
+++ b/dlls/oledb32/oledb_private.h
@@ -23,7 +23,7 @@ HRESULT create_error_info(IUnknown *outer, void **obj);
 HRESULT create_oledb_rowpos(IUnknown *outer, void **obj);
 HRESULT create_dslocator(IUnknown *outer, void **obj);
 
-HRESULT get_data_source(IUnknown *outer, DWORD clsctx, LPWSTR initstring, REFIID riid,
+HRESULT get_data_source(IUnknown *outer, DWORD clsctx, LPCOLESTR initstring, REFIID riid,
     IUnknown **datasource);
 
 extern HINSTANCE instance;
diff --git a/include/msdasc.idl b/include/msdasc.idl
index 6a904ba1d2f..98d3f2abb50 100644
--- a/include/msdasc.idl
+++ b/include/msdasc.idl
@@ -92,7 +92,7 @@ library MSDASC
     interface IDataInitialize : IUnknown
     {
         HRESULT GetDataSource([in] IUnknown* pUnkOuter, [in]  DWORD dwClsCtx,
-                        [in] LPWSTR pwszInitializationString, [in] REFIID riid,
+                        [in] LPCOLESTR pwszInitializationString, [in] REFIID riid,
                         [in, out] IUnknown** ppDataSource);
 
         HRESULT GetInitializationString([in] IUnknown* pDataSource, [in] boolean fIncludePassword,
@@ -113,9 +113,9 @@ library MSDASC
                         [in] DWORD cmq,  [in, size_is(cmq)] const IID **iids, [out, size_is(cmq)] IUnknown **ifs,
                         [out, size_is(cmq)] HRESULT *hr);
 
-        HRESULT LoadStringFromStorage([in] LPWSTR pwszFileName, [out] LPWSTR* ppwszInitializationString);
+        HRESULT LoadStringFromStorage([in] LPCOLESTR pwszFileName, [out] LPOLESTR *ppwszInitializationString);
 
-        HRESULT WriteStringToStorage([in] LPWSTR pwszFileName,  [in] LPWSTR pwszInitializationString,
+        HRESULT WriteStringToStorage([in] LPCOLESTR pwszFileName, [in] LPCOLESTR pwszInitializationString,
                         [in] DWORD dwCreationDisposition);
     }