diff --git a/lib/capn-malloc.c b/lib/capn-malloc.c
index 7a2977c..525ae99 100644
--- a/lib/capn-malloc.c
+++ b/lib/capn-malloc.c
@@ -14,6 +14,11 @@
 #include <limits.h>
 #include <errno.h>
 
+/* Visual Studio notes:
+ * Unless capn_segment is defined with __declspec(align(64)), check_segment_alignment
+ * Fails to compile in x86 mode, as (sizeof(struct capn_segment)&7) -> (44 & 7) evaluates to 4
+ * Compiles in x64 mode, as (sizeof(struct capn_segment)&7) -> (80 & 7) evaluates to 0 
+ */
 struct check_segment_alignment {
 	unsigned int foo : (sizeof(struct capn_segment)&7) ? -1 : 1;
 };
diff --git a/lib/capnp_c.h b/lib/capnp_c.h
index 5ccf0f5..40432ba 100644
--- a/lib/capnp_c.h
+++ b/lib/capnp_c.h
@@ -100,6 +100,9 @@ struct capn_tree *capn_tree_insert(struct capn_tree *root, struct capn_tree *n);
  * data, len, cap, and user should all set by the user. Other values
  * should be zero initialized.
  */
+#ifdef _MSC_VER
+__declspec(align(64))
+#endif
 struct capn_segment {
 	struct capn_tree hdr;
 	struct capn_segment *next;