diff --git a/inc/vmapi/hf/spci.h b/inc/vmapi/hf/spci.h
index 977c4a4..da3ad48 100644
--- a/inc/vmapi/hf/spci.h
+++ b/inc/vmapi/hf/spci.h
@@ -233,6 +233,8 @@
 	uint32_t address_high;
 	/** The number of 4 kiB pages in the constituent memory region. */
 	uint32_t page_count;
+	/** Reserved field, must be 0. */
+	uint32_t reserved;
 };
 
 struct spci_memory_region_attributes {
@@ -243,6 +245,10 @@
 	 * receiver's page table.
 	 */
 	uint16_t memory_attributes;
+	/** Reserved field, must be 0. */
+	uint32_t reserved_0;
+	/** Reserved field, must be 0. */
+	uint64_t reserved_1;
 };
 
 /** Flags to control the behaviour of a memory sharing transaction. */
@@ -265,7 +271,7 @@
 	/** Sender VM ID. */
 	spci_vm_id_t sender;
 	/** Reserved field, must be 0. */
-	uint16_t reserved;
+	uint16_t reserved_0;
 	/**
 	 * The total number of 4 kiB pages included in this memory region. This
 	 * must be equal to the sum of page counts specified in each
@@ -288,6 +294,8 @@
 	 * this memory region.
 	 */
 	uint32_t attribute_count;
+	/** Reserved field, must be 0. */
+	uint16_t reserved_1;
 	/**
 	 * An array of `attribute_count` memory region attribute descriptors.
 	 * Each one specifies an endpoint and the attributes with which this
diff --git a/vmlib/spci.c b/vmlib/spci.c
index 37447e4..e5fccba 100644
--- a/vmlib/spci.c
+++ b/vmlib/spci.c
@@ -56,12 +56,15 @@
 	memory_region->tag = tag;
 	memory_region->flags = flags;
 	memory_region->sender = sender;
-	memory_region->reserved = 0;
+	memory_region->reserved_0 = 0;
+	memory_region->reserved_1 = 0;
 	memory_region->page_count = 0;
 	memory_region->constituent_count = constituent_count;
 	memory_region->attribute_count = 1;
 	memory_region->attributes[0].receiver = receiver;
 	memory_region->attributes[0].memory_attributes = attributes;
+	memory_region->attributes[0].reserved_0 = 0;
+	memory_region->attributes[0].reserved_1 = 0;
 
 	/*
 	 * Constituent offset must be aligned to a 32-bit boundary so that