diff --git a/reactos/ntoskrnl/include/internal/arm/mm.h b/reactos/ntoskrnl/include/internal/arm/mm.h
index 83b553fe6a5..5d24793cb16 100644
--- a/reactos/ntoskrnl/include/internal/arm/mm.h
+++ b/reactos/ntoskrnl/include/internal/arm/mm.h
@@ -166,4 +166,7 @@ typedef enum _ARM_DOMAIN
 #define PDE_BASE    0xC1000000
 #define HYPER_SPACE 0xC1100000
 
+struct _EPROCESS;
+PULONG MmGetPageDirectory(VOID);
+
 #endif
diff --git a/reactos/ntoskrnl/include/internal/i386/mm.h b/reactos/ntoskrnl/include/internal/i386/mm.h
index 44867629e4b..ce83e73c497 100644
--- a/reactos/ntoskrnl/include/internal/i386/mm.h
+++ b/reactos/ntoskrnl/include/internal/i386/mm.h
@@ -5,6 +5,8 @@
 #ifndef __NTOSKRNL_INCLUDE_INTERNAL_I386_MM_H
 #define __NTOSKRNL_INCLUDE_INTERNAL_I386_MM_H
 
+#ifdef _M_IX86
+
 struct _EPROCESS;
 PULONG MmGetPageDirectory(VOID);
 
@@ -28,4 +30,6 @@ PULONG MmGetPageDirectory(VOID);
 /* Easy accessing PFN in PTE */
 #define PFN_FROM_PTE(v) ((v)->u.Hard.PageFrameNumber)
 
+#endif
+
 #endif /* __NTOSKRNL_INCLUDE_INTERNAL_I386_MM_H */