diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
index b02cc02e75..3297f27684 100644
--- a/xen/arch/arm/efi/efi-boot.h
+++ b/xen/arch/arm/efi/efi-boot.h
@@ -370,16 +370,14 @@ static void __init efi_arch_cfg_file_late(EFI_FILE_HANDLE dir_handle, char *sect
 {
 }
 
-static void *__init efi_arch_allocate_mmap_buffer(UINTN *map_size)
+static void *__init efi_arch_allocate_mmap_buffer(UINTN map_size)
 {
     void *ptr;
     EFI_STATUS status;
-    UINTN map_size_alloc = *map_size + EFI_PAGE_SIZE;
 
-    status = efi_bs->AllocatePool(EfiLoaderData, map_size_alloc, &ptr);
+    status = efi_bs->AllocatePool(EfiLoaderData, map_size, &ptr);
     if ( status != EFI_SUCCESS )
         return NULL;
-    *map_size = map_size_alloc;
     return ptr;
 }
 
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index 3a3b4fe3b8..cd14c19bf2 100644
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -190,10 +190,10 @@ static void __init efi_arch_process_memory_map(EFI_SYSTEM_TABLE *SystemTable,
 
 }
 
-static void *__init efi_arch_allocate_mmap_buffer(UINTN *map_size)
+static void *__init efi_arch_allocate_mmap_buffer(UINTN map_size)
 {
     place_string(&mbi.mem_upper, NULL);
-    mbi.mem_upper -= *map_size;
+    mbi.mem_upper -= map_size;
     mbi.mem_upper &= -__alignof__(EFI_MEMORY_DESCRIPTOR);
     if ( mbi.mem_upper < xen_phys_start )
         return NULL;
diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index ef8476c676..60c1b8dc32 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -700,7 +700,7 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
     EFI_STATUS status;
     unsigned int i, argc;
     CHAR16 **argv, *file_name, *cfg_file_name = NULL, *options = NULL;
-    UINTN map_key, info_size, gop_mode = ~0;
+    UINTN map_alloc_size, map_key, info_size, gop_mode = ~0;
     EFI_HANDLE *handles = NULL;
     EFI_SHIM_LOCK_PROTOCOL *shim_lock;
     EFI_GRAPHICS_OUTPUT_PROTOCOL *gop = NULL;
@@ -1053,14 +1053,16 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
             efi_arch_video_init(gop, info_size, mode_info);
     }
 
-    efi_bs->GetMemoryMap(&efi_memmap_size, NULL, &map_key,
+    efi_bs->GetMemoryMap(&map_alloc_size, NULL, &map_key,
                          &efi_mdesc_size, &mdesc_ver);
-    efi_memmap = efi_arch_allocate_mmap_buffer(&efi_memmap_size);
+    map_alloc_size += 8 * efi_mdesc_size;
+    efi_memmap = efi_arch_allocate_mmap_buffer(map_alloc_size);
     if ( !efi_memmap )
         blexit(L"Unable to allocate memory for EFI memory map");
 
     for ( retry = 0; ; retry = 1 )
     {
+        efi_memmap_size = map_alloc_size;
         status = efi_bs->GetMemoryMap(&efi_memmap_size, efi_memmap, &map_key,
                                       &efi_mdesc_size, &mdesc_ver);
         if ( EFI_ERROR(status) )