diff --git a/reactos/include/ddk/ntdef.h b/reactos/include/ddk/ntdef.h
index 303e6e50b6f..33a6500170c 100644
--- a/reactos/include/ddk/ntdef.h
+++ b/reactos/include/ddk/ntdef.h
@@ -140,6 +140,7 @@ typedef unsigned long POINTER_64; // FIXME! HACK!!!
 
 
 // FIXME
+#undef UNALIGNED
 #define UNALIGNED
 #define RESTRICTED_POINTER
 
diff --git a/reactos/include/ddk/ntifs.h b/reactos/include/ddk/ntifs.h
index 025ee5e8e84..1c94a6ce814 100644
--- a/reactos/include/ddk/ntifs.h
+++ b/reactos/include/ddk/ntifs.h
@@ -4751,7 +4751,7 @@ NTAPI
 RtlAllocateHeap (
     IN HANDLE  HeapHandle,
     IN ULONG   Flags,
-    IN ULONG   Size
+    IN SIZE_T   Size
 );
 
 NTSYSAPI
diff --git a/reactos/include/ddk/ntimage.h b/reactos/include/ddk/ntimage.h
index 716563968e3..e008a2daa94 100644
--- a/reactos/include/ddk/ntimage.h
+++ b/reactos/include/ddk/ntimage.h
@@ -480,7 +480,7 @@ typedef struct _IMAGE_THUNK_DATA32 {
     } u1;
 } IMAGE_THUNK_DATA32, *PIMAGE_THUNK_DATA32;
 
-#define IMAGE_ORDINAL_FLAG64 0x8000000000000000
+#define IMAGE_ORDINAL_FLAG64 0x8000000000000000ULL
 #define IMAGE_ORDINAL_FLAG32 0x80000000
 #define IMAGE_ORDINAL64(Ordinal) (Ordinal & 0xffff)
 #define IMAGE_ORDINAL32(Ordinal) (Ordinal & 0xffff)
diff --git a/reactos/include/ndk/rtlfuncs.h b/reactos/include/ndk/rtlfuncs.h
index 8203b5e600f..1a164efe379 100644
--- a/reactos/include/ndk/rtlfuncs.h
+++ b/reactos/include/ndk/rtlfuncs.h
@@ -481,7 +481,7 @@ NTAPI
 RtlAllocateHeap(
     IN HANDLE HeapHandle,
     IN ULONG Flags,
-    IN ULONG Size
+    IN SIZE_T Size
 );
 
 NTSYSAPI
@@ -539,7 +539,7 @@ RtlExtendHeap(
     IN HANDLE Heap,
     IN ULONG Flags,
     IN PVOID P,
-    IN ULONG Size
+    IN SIZE_T Size
 );
 
 NTSYSAPI
@@ -646,7 +646,7 @@ RtlSetUserFlagsHeap(
 );
 
 NTSYSAPI
-ULONG
+SIZE_T
 NTAPI
 RtlSizeHeap(
     IN PVOID HeapHandle,