diff --git a/reactos/dll/win32/setupapi/stringtable.c b/reactos/dll/win32/setupapi/stringtable.c
index b143cd5f0bc..9eba15fb977 100644
--- a/reactos/dll/win32/setupapi/stringtable.c
+++ b/reactos/dll/win32/setupapi/stringtable.c
@@ -602,13 +602,13 @@ StringTableLookUpStringEx(HSTRING_TABLE hStringTable,
                           LPWSTR lpString,
                           DWORD dwFlags,
                           LPVOID lpExtraData,
-                          LPDWORD lpReserved)
+                          DWORD dwReserved)
 {
     PSTRING_TABLE pStringTable;
     DWORD i;
 
     TRACE("%p %s %x %p, %x\n", hStringTable, debugstr_w(lpString), dwFlags,
-          lpExtraData, lpReserved);
+          lpExtraData, dwReserved);
 
     pStringTable = (PSTRING_TABLE)hStringTable;
     if (pStringTable == NULL)
@@ -627,11 +627,7 @@ StringTableLookUpStringEx(HSTRING_TABLE hStringTable,
                 if (!lstrcmpW(pStringTable->pSlots[i].pString, lpString))
                 {
                     if (lpExtraData)
-                    {
-                        memcpy(lpExtraData,
-                               pStringTable->pSlots[i].pData,
-                               pStringTable->pSlots[i].dwSize);
-                    }
+                        memcpy(lpExtraData, pStringTable->pSlots[i].pData, dwReserved);
                     return i + 1;
                 }
             }
@@ -640,18 +636,13 @@ StringTableLookUpStringEx(HSTRING_TABLE hStringTable,
                 if (!lstrcmpiW(pStringTable->pSlots[i].pString, lpString))
                 {
                     if (lpExtraData)
-                    {
-                        memcpy(lpExtraData,
-                               pStringTable->pSlots[i].pData,
-                               pStringTable->pSlots[i].dwSize);
-                    }
+                        memcpy(lpExtraData, pStringTable->pSlots[i].pData, dwReserved);
                     return i + 1;
                 }
             }
         }
     }
-
-    return (DWORD)-1;
+    return ~0u;
 }
 
 
diff --git a/reactos/include/psdk/setupapi.h b/reactos/include/psdk/setupapi.h
index 4e039da25ab..e53555c9f7c 100644
--- a/reactos/include/psdk/setupapi.h
+++ b/reactos/include/psdk/setupapi.h
@@ -1434,7 +1434,7 @@ WINSETUPAPI BOOL   WINAPI StringTableGetExtraData(HSTRING_TABLE, DWORD, LPVOID,
 WINSETUPAPI HSTRING_TABLE WINAPI StringTableInitialize(VOID);
 WINSETUPAPI HSTRING_TABLE WINAPI StringTableInitializeEx(DWORD, DWORD);
 WINSETUPAPI DWORD  WINAPI StringTableLookUpString(HSTRING_TABLE, LPWSTR, DWORD);
-WINSETUPAPI DWORD  WINAPI StringTableLookUpStringEx(HSTRING_TABLE, LPWSTR, DWORD, LPVOID, LPDWORD);
+WINSETUPAPI DWORD  WINAPI StringTableLookUpStringEx(HSTRING_TABLE, LPWSTR, DWORD, LPVOID, DWORD);
 WINSETUPAPI BOOL   WINAPI StringTableSetExtraData(HSTRING_TABLE, DWORD, LPVOID, DWORD);
 WINSETUPAPI LPWSTR WINAPI StringTableStringFromId(HSTRING_TABLE, DWORD);
 WINSETUPAPI BOOL   WINAPI StringTableStringFromIdEx(HSTRING_TABLE, DWORD, LPWSTR, LPDWORD);