diff --git a/include/wine/library.h b/include/wine/library.h
index 52186c612f2..110239029b6 100644
--- a/include/wine/library.h
+++ b/include/wine/library.h
@@ -135,6 +135,9 @@ static inline void wine_ldt_set_base( LDT_ENTRY *ent, const void *base )
     ent->BaseLow               = (WORD)(ULONG_PTR)base;
     ent->HighWord.Bits.BaseMid = (BYTE)((ULONG_PTR)base >> 16);
     ent->HighWord.Bits.BaseHi  = (BYTE)((ULONG_PTR)base >> 24);
+#ifdef _WIN64
+    ent->BaseHigh              = (ULONG_PTR)base >> 32;
+#endif
 }
 static inline void wine_ldt_set_limit( LDT_ENTRY *ent, unsigned int limit )
 {
@@ -145,6 +148,9 @@ static inline void wine_ldt_set_limit( LDT_ENTRY *ent, unsigned int limit )
 static inline void *wine_ldt_get_base( const LDT_ENTRY *ent )
 {
     return (void *)(ent->BaseLow |
+#ifdef _WIN64
+                    (ULONG_PTR)ent->BaseHigh << 32 |
+#endif
                     (ULONG_PTR)ent->HighWord.Bits.BaseMid << 16 |
                     (ULONG_PTR)ent->HighWord.Bits.BaseHi << 24);
 }
diff --git a/include/winnt.h b/include/winnt.h
index 083bd961701..580c2e55d09 100644
--- a/include/winnt.h
+++ b/include/winnt.h
@@ -846,6 +846,9 @@ typedef struct _LDT_ENTRY {
             unsigned    BaseHi : 8;
         } Bits;
     } HighWord;
+#ifdef _WIN64  /* FIXME: 64-bit code should not be using the LDT */
+    DWORD BaseHigh;
+#endif
 } LDT_ENTRY, *PLDT_ENTRY;
 
 /* x86-64 context definitions */