diff --git a/CHANGES.md b/CHANGES.md
index 02b59d1..4941178 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -8,6 +8,7 @@
 * Fix sign extensions (#49, @rixed)
 * `Long_val` returns `intnat`, previously `long` was used (#53, @dra27)
 * Reduce size of marshalled custom values on 4.08+ (#54, @dra27)
+* Store 128-bit ints as structs to prevent unaligned access (#55, @dra27)
 
 ## New features:
 
diff --git a/lib/int128.h b/lib/int128.h
index 194e1ae..3b7e73e 100644
--- a/lib/int128.h
+++ b/lib/int128.h
@@ -2,14 +2,27 @@
 #define OCAML_INT128_H
 
 #if defined(__SIZEOF_INT128__) 
+
 #define HAVE_INT128
 typedef __int128_t int128;
+typedef struct { uint64_t low; int64_t high; } int128_ocaml;
+
+inline __int128_t get_int128(value v)
+{
+  int128_ocaml *i = (int128_ocaml *)Data_custom_val(v);
+  return ((__int128_t)i->high << 64 | i->low);
+}
+
+#define Int128_val(v) get_int128(v)
+
 #else
+
 typedef struct { int64_t high; uint64_t low; } int128;
-#endif
 
 #define Int128_val(v) (*((int128 *)Data_custom_val(v)))
 
+#endif
+
 CAMLextern value copy_int128(int128 i);
 
 #endif
diff --git a/lib/int128_stubs.c b/lib/int128_stubs.c
index ad85a3d..b48483c 100644
--- a/lib/int128_stubs.c
+++ b/lib/int128_stubs.c
@@ -147,6 +147,18 @@ struct custom_operations int128_ops = {
 #endif
 };
 
+#ifdef HAVE_INT128
+CAMLprim value
+copy_int128(__int128_t i)
+{
+  CAMLparam0();
+  value res = caml_alloc_custom(&int128_ops, 16, 0, 1);
+  int128_ocaml *v = (int128_ocaml *)Data_custom_val(res);
+  v->high = (int64_t)(i >> 64);
+  v->low = (uint64_t)i;
+  CAMLreturn (res);
+}
+#else
 CAMLprim value
 copy_int128(int128 i)
 {
@@ -155,6 +167,7 @@ copy_int128(int128 i)
   Int128_val(res) = i;
   CAMLreturn (res);
 }
+#endif
 
 CAMLprim value
 int128_add(value v1, value v2)
diff --git a/lib/uint128.h b/lib/uint128.h
index 3f97dab..ae9292f 100644
--- a/lib/uint128.h
+++ b/lib/uint128.h
@@ -2,14 +2,27 @@
 #define OCAML_UINT128_H
 
 #if defined(__SIZEOF_INT128__) 
+
 #define HAVE_UINT128
 typedef __uint128_t uint128;
+typedef struct { uint64_t low; uint64_t high; } uint128_ocaml;
+
+inline __uint128_t get_uint128(value v)
+{
+  uint128_ocaml *i = (uint128_ocaml *)Data_custom_val(v);
+  return ((__uint128_t)i->high << 64 | i->low);
+}
+
+#define Uint128_val(v) get_uint128(v)
+
 #else
+
 typedef struct { uint64_t high; uint64_t low; } uint128;
-#endif
 
 #define Uint128_val(v) (*((uint128 *)Data_custom_val(v)))
 
+#endif
+
 CAMLextern value copy_uint128(uint128 i);
 CAMLextern value suint128_add(value v1, value v2, CAMLprim value (*)(uint128));
 CAMLextern value suint128_sub(value v1, value v2, CAMLprim value (*)(uint128));
@@ -20,4 +33,3 @@ CAMLextern value suint128_xor(value v1, value v2, CAMLprim value (*)(uint128));
 CAMLextern value suint128_shift_left(value v1, value v2, CAMLprim value (*)(uint128));
 
 #endif
-
diff --git a/lib/uint128_stubs.c b/lib/uint128_stubs.c
index 3465bd3..bf10a17 100644
--- a/lib/uint128_stubs.c
+++ b/lib/uint128_stubs.c
@@ -189,6 +189,18 @@ struct custom_operations uint128_ops = {
 #endif
 };
 
+#ifdef HAVE_UINT128
+CAMLprim value
+copy_uint128(__uint128_t i)
+{
+  CAMLparam0();
+  value res = caml_alloc_custom(&uint128_ops, 16, 0, 1);
+  uint128_ocaml *v = (uint128_ocaml *)Data_custom_val(res);
+  v->high = (uint64_t)(i >> 64);
+  v->low = (uint64_t)i;
+  CAMLreturn (res);
+}
+#else
 CAMLprim value
 copy_uint128(uint128 i)
 {
@@ -197,6 +209,7 @@ copy_uint128(uint128 i)
   Uint128_val(res) = i;
   CAMLreturn (res);
 }
+#endif
 
 CAMLprim value
 suint128_add(value v1, value v2, CAMLprim value (*copy)(uint128))