diff --git a/ml-proto/spec/check.ml b/ml-proto/spec/check.ml
index 03a4ba155e..a339dd58cf 100644
--- a/ml-proto/spec/check.ml
+++ b/ml-proto/spec/check.ml
@@ -216,18 +216,18 @@ let rec check_expr c et e =
     check_type None et e.at
 
   | Load (memop, e1) ->
-    check_load c et memop e1 e.at
+    check_load c et memop (size memop.ty) e1 e.at
 
   | Store (memop, e1, e2) ->
-    check_store c et memop e1 e2 e.at
+    check_store c et memop (size memop.ty) e1 e2 e.at
 
   | LoadExtend (extendop, e1) ->
     check_mem_type extendop.memop.ty extendop.sz e.at;
-    check_load c et extendop.memop e1 e.at
+    check_load c et extendop.memop (Memory.mem_size extendop.sz) e1 e.at
 
   | StoreWrap (wrapop, e1, e2) ->
     check_mem_type wrapop.memop.ty wrapop.sz e.at;
-    check_store c et wrapop.memop e1 e2 e.at
+    check_store c et wrapop.memop (Memory.mem_size wrapop.sz) e1 e2 e.at
 
   | Const v ->
     check_literal c et v
@@ -279,24 +279,24 @@ and check_expr_opt c et eo at =
 and check_literal c et l =
   check_type (Some (type_value l.it)) et l.at
 
-and check_load c et memop e1 at =
+and check_load c et memop mem_size e1 at =
   ignore (memory c at);
-  check_memop memop at;
+  check_memop memop mem_size at;
   check_expr c (some Int32Type) e1;
   check_type (Some memop.ty) et at
 
-and check_store c et memop e1 e2 at =
+and check_store c et memop mem_size e1 e2 at =
   ignore (memory c at);
-  check_memop memop at;
+  check_memop memop mem_size at;
   check_expr c (some Int32Type) e1;
   check_expr c (some memop.ty) e2;
   check_type None et at
 
-and check_memop memop at =
+and check_memop memop mem_size at =
   require (memop.offset >= 0L) at "negative offset";
   require (memop.offset <= 0xffffffffL) at "offset too large";
   require (Lib.Int.is_power_of_two memop.align) at "alignment must be a power of two";
-  require (memop.align <= size memop.ty) at "alignment must not be larger than natural"
+  require (memop.align <= mem_size) at "alignment must not be larger than natural"
 
 and check_mem_type ty sz at =
   require (ty = Int64Type || sz <> Memory.Mem32) at "memory size too big"
diff --git a/ml-proto/spec/memory.ml b/ml-proto/spec/memory.ml
index 0cf43e3107..536638f241 100644
--- a/ml-proto/spec/memory.ml
+++ b/ml-proto/spec/memory.ml
@@ -24,6 +24,11 @@ exception OutOfMemory
 
 let page_size = 0x10000L (* 64 KiB *)
 
+let mem_size = function
+  | Mem8 -> 1
+  | Mem16 -> 2
+  | Mem32 -> 4
+
 (*
  * These limitations should be considered part of the host environment and not
  * part of the spec defined by this file.
diff --git a/ml-proto/spec/memory.mli b/ml-proto/spec/memory.mli
index 988637e9f6..b0695ed936 100644
--- a/ml-proto/spec/memory.mli
+++ b/ml-proto/spec/memory.mli
@@ -19,6 +19,8 @@ exception OutOfMemory
 
 val page_size : offset
 
+val mem_size : mem_size -> int
+
 val create : size -> size option -> memory (* raise SizeOverflow, OutOfMemory *)
 val size : memory -> size
 val grow : memory -> size -> unit (* raise SizeOverflow, OutOfMemory *)
diff --git a/ml-proto/test/memory.wast b/ml-proto/test/memory.wast
index 1170ade959..dbf6335976 100644
--- a/ml-proto/test/memory.wast
+++ b/ml-proto/test/memory.wast
@@ -85,8 +85,8 @@
 )
 
 ;; Test alignment annotation rules
-(module (memory 0) (func (drop (i32.load8_u align=2 (i32.const 0)))))
-(module (memory 0) (func (drop (i32.load16_u align=4 (i32.const 0)))))
+(module (memory 0) (func (drop (i32.load8_u align=1 (i32.const 0)))))
+(module (memory 0) (func (drop (i32.load16_u align=2 (i32.const 0)))))
 (module (memory 0) (func (drop (i32.load align=4 (i32.const 0)))))
 (module (memory 0) (func (drop (f32.load align=4 (i32.const 0)))))
 
@@ -112,15 +112,27 @@
 )
 
 (assert_invalid
-  (module (memory 0) (func (i64.load align=16 (i32.const 0))))
+  (module (memory 0) (func (drop (i64.load align=16 (i32.const 0)))))
   "alignment must not be larger than natural"
 )
 (assert_invalid
-  (module (memory 0) (func (i64.load align=32 (i32.const 0))))
+  (module (memory 0) (func (drop (i64.load align=32 (i32.const 0)))))
   "alignment must not be larger than natural"
 )
 (assert_invalid
-  (module (memory 0) (func (i32.load align=8 (i32.const 0))))
+  (module (memory 0) (func (drop (i32.load align=8 (i32.const 0)))))
+  "alignment must not be larger than natural"
+)
+(assert_invalid
+  (module (memory 0) (func (drop (i32.load16_u align=4 (i32.const 0)))))
+  "alignment must not be larger than natural"
+)
+(assert_invalid
+  (module (memory 0) (func (drop (i32.load8_u align=2 (i32.const 0)))))
+  "alignment must not be larger than natural"
+)
+(assert_invalid
+  (module (memory 0) (func (i32.store8 align=2 (i32.const 0) (i32.const 0))))
   "alignment must not be larger than natural"
 )