diff --git a/interpreter/runtime/memory.ml b/interpreter/runtime/memory.ml
index 9e73d6d2a..db32ae56d 100644
--- a/interpreter/runtime/memory.ml
+++ b/interpreter/runtime/memory.ml
@@ -17,17 +17,18 @@ exception SizeOverflow
 exception SizeLimit
 exception OutOfMemory
 
-let page_size = 0x10000L (* 64 KiB *)
-
 let valid_limits {min; max} =
   match max with
   | None -> true
   | Some m -> I64.le_u min m
 
-let valid_size at i =
-  match at with
-  | I32AT -> I64.le_u i 0xffffL
-  | I64AT -> true
+let valid_size at pt i =
+  match pt with
+  | PageT 1 -> true
+  | PageT ps ->
+     match at with
+     | I32AT -> I64.le_u i (Int64.div 0xffffffffL (Int64.of_int ps))
+     | I64AT -> true
 
 let create n (PageT ps) =
   try
@@ -39,7 +40,7 @@ let create n (PageT ps) =
 
 let alloc (MemoryT (at, lim, pt) as ty) =
   assert Free.((memorytype ty).types = Set.empty);
-  if not (valid_size at lim.min) then raise SizeOverflow;
+  if not (valid_size at pt lim.min) then raise SizeOverflow;
   if not (valid_limits lim) then raise Type;
   {ty; content = create lim.min pt}
 
@@ -65,7 +66,7 @@ let grow mem delta =
   let new_size = Int64.add old_size delta in
   if I64.gt_u old_size new_size then raise SizeOverflow else
   let lim' = {lim with min = new_size} in
-  if not (valid_size at new_size) then raise SizeOverflow else
+  if not (valid_size at pt new_size) then raise SizeOverflow else
   if not (valid_limits lim') then raise SizeLimit else
   let after = create new_size pt in
   let dim = Array1_64.dim mem.content in
diff --git a/interpreter/runtime/memory.mli b/interpreter/runtime/memory.mli
index 5bbc8a77e..0dae66766 100644
--- a/interpreter/runtime/memory.mli
+++ b/interpreter/runtime/memory.mli
@@ -14,8 +14,6 @@ exception SizeOverflow
 exception SizeLimit
 exception OutOfMemory
 
-val page_size : int64
-
 val alloc : memorytype -> memory (* raises Type, SizeOverflow, OutOfMemory *)
 val type_of : memory -> memorytype
 val addrtype_of : memory -> addrtype
diff --git a/interpreter/text/lexer.mll b/interpreter/text/lexer.mll
index 653c93a5b..f11ba87b1 100644
--- a/interpreter/text/lexer.mll
+++ b/interpreter/text/lexer.mll
@@ -780,6 +780,7 @@ rule token = parse
       | "start" -> START
       | "import" -> IMPORT
       | "export" -> EXPORT
+      | "pagesize" -> PAGESIZE
 
       | "module" -> MODULE
       | "binary" -> BIN
diff --git a/interpreter/text/parser.mly b/interpreter/text/parser.mly
index 0ee8020c3..19c94aec1 100644
--- a/interpreter/text/parser.mly
+++ b/interpreter/text/parser.mly
@@ -321,6 +321,7 @@ let parse_annots (m : module_) : Custom.section list =
 %token VEC_SHUFFLE
 %token<Ast.laneidx -> Ast.instr'> VEC_EXTRACT VEC_REPLACE
 %token FUNC START TYPE PARAM RESULT LOCAL GLOBAL
+%token PAGESIZE
 %token TABLE ELEM MEMORY TAG DATA DECLARE OFFSET ITEM IMPORT EXPORT
 %token MODULE BIN QUOTE DEFINITION INSTANCE
 %token SCRIPT REGISTER INVOKE GET
@@ -465,8 +466,21 @@ subtype :
 tabletype :
   | addrtype limits reftype { fun c -> TableT ($1, $2, $3 c) }
 
+pagetype :
+  | LPAR PAGESIZE NAT RPAR
+    { let v' =
+        try (int_of_string $3)
+        with Failure _ ->
+          error (at $sloc) "invalid custom page size"
+      in
+      if not (v' > 0 && Lib.Int.is_power_of_two v') then
+        error (at $sloc) "invalid custom page size";
+      PageT v'
+    }
+
 memorytype :
   | addrtype limits { fun c -> MemoryT ($1, $2, PageT 0x10000) }
+  | addrtype limits pagetype { fun c -> MemoryT ($1, $2, $3) }
 
 limits :
   | NAT { {min = nat64 $1 $loc($1); max = None} }
@@ -1126,15 +1140,19 @@ memory_fields :
   | inline_export memory_fields  /* Sugar */
     { fun c x loc -> let mems, data, ims, exs = $2 c x loc in
       mems, data, ims, $1 (MemoryX x) c :: exs }
-  | addrtype LPAR DATA string_list RPAR  /* Sugar */
+  | addrtype pagetype LPAR DATA string_list RPAR  /* Sugar */
     { fun c x loc ->
-      let size = Int64.(div (add (of_int (String.length $4)) 65535L) 65536L) in
+      let len64 = Int64.of_int (String.length $5) in
+      let size =
+        match $2 with
+        | PageT 0 -> len64 (* will be a validation error *)
+        | PageT 1 -> len64
+        | PageT ps -> Int64.(div (add len64 (sub (of_int ps) 1L)) (of_int ps)) in
       let offset = [at_const $1 (0L @@ loc) @@ loc] @@ loc in
-      [Memory (MemoryT ($1, {min = size; max = Some size}, PageT 0x10000)) @@ loc],
-      [Data ($4, Active (x, offset) @@ loc) @@ loc],
+      [Memory (MemoryT ($1, {min = size; max = Some size}, $2)) @@ loc],
+      [Data ($5, Active (x, offset) @@ loc) @@ loc],
       [], [] }
 
-
 elemkind :
   | FUNC { (NoNull, FuncHT) }
 
diff --git a/interpreter/valid/valid.ml b/interpreter/valid/valid.ml
index c22a1d0cf..f1bb83145 100644
--- a/interpreter/valid/valid.ml
+++ b/interpreter/valid/valid.ml
@@ -105,7 +105,7 @@ let check_limits {min; max} range at msg =
       "size minimum must not be greater than maximum"
 
 let check_pagetype (PageT ps) at =
-  require (ps = 0x10000 || ps = 1) at "page size must be 1 or 64KiB"
+  require (ps = 0x10000 || ps = 1) at "invalid custom page size"
 
 let check_numtype (c : context) (t : numtype) at =
   ()
@@ -200,13 +200,19 @@ let check_globaltype (c : context) (gt : globaltype) at =
 
 let check_memorytype (c : context) (mt : memorytype) at =
   let MemoryT (at_, lim, pt) = mt in
+  check_pagetype pt at;
   let sz, s =
-    match at_ with
-    | I32AT -> 0x1_0000L, "2^16 pages (4 GiB) for i32"
-    | I64AT -> 0x1_0000_0000_0000L, "2^48 pages (256 TiB) for i64"
+    match pt with
+    | PageT 0x10000 ->
+       (match at_ with
+       | I32AT -> 0x1_0000L, "2^16 pages (4 GiB) for i32"
+       | I64AT -> 0x1_0000_0000_0000L, "2^48 pages (256 TiB) for i64")
+    | _ -> (* TODO: divide by page size, what about error msg? *)
+       (match at_ with
+       | I32AT -> 0xFFFF_FFFFL, "2^32 - 1 bytes for i32"
+       | I64AT -> 0xFFFF_FFFF_FFFF_FFFFL, "2^64 - 1 bytes for i64")
   in
-  check_limits lim sz at ("memory size must be at most " ^ s);
-  check_pagetype pt at
+  check_limits lim sz at ("memory size must be at most " ^ s)
 
 let check_tabletype (c : context) (tt : tabletype) at =
   let TableT (at_, lim, t) = tt in
diff --git a/test/core/custom-page-sizes/custom-page-sizes.wast b/test/core/custom-page-sizes/custom-page-sizes.wast
index 332051daa..b8ffd34e8 100644
--- a/test/core/custom-page-sizes/custom-page-sizes.wast
+++ b/test/core/custom-page-sizes/custom-page-sizes.wast
@@ -110,7 +110,7 @@
 ;; Inline data segments
 
 ;; pagesize 0
-(assert_malformed (module quote "(memory (pagesize 0) (data))") "invalid custom page size")
+(assert_malformed (module quote "(module (memory (pagesize 0) (data)))") "invalid custom page size")
 
 ;; pagesize 1
 (module
diff --git a/test/core/custom-page-sizes/memory_max.wast b/test/core/custom-page-sizes/memory_max.wast
index 7f3b497d6..5ae6fe814 100644
--- a/test/core/custom-page-sizes/memory_max.wast
+++ b/test/core/custom-page-sizes/memory_max.wast
@@ -19,14 +19,26 @@
   (module
     (import "test" "unknown" (func))
     (memory 0xFFFF_FFFF (pagesize 1)))
-  "unknown import")
+  "incompatible import type")
+
+;; i32 (pagesize 1)
+(assert_unlinkable
+  (module
+    (import "test" "unknown" (memory 0xFFFF_FFFF (pagesize 1))))
+  "incompatible import type")
 
 ;; i32 (default pagesize)
 (assert_unlinkable
   (module
     (import "test" "unknown" (func))
     (memory 65536 (pagesize 65536)))
-  "unknown import")
+  "incompatible import type")
+
+;; i32 (default pagesize)
+(assert_unlinkable
+  (module
+    (import "test" "unknown" (memory 65536 (pagesize 65536))))
+  "incompatible import type")
 
 ;; Memory size just over the maximum.
 
diff --git a/test/core/custom-page-sizes/memory_max_i64.wast b/test/core/custom-page-sizes/memory_max_i64.wast
index 81e9aaf5c..cb18fc62b 100644
--- a/test/core/custom-page-sizes/memory_max_i64.wast
+++ b/test/core/custom-page-sizes/memory_max_i64.wast
@@ -17,16 +17,28 @@
 ;; i64 (pagesize 1)
 (assert_unlinkable
   (module
-    (import "test" "import" (func))
+    (import "test" "unknown" (func))
     (memory i64 0xFFFF_FFFF_FFFF_FFFF (pagesize 1)))
-  "unknown import")
+  "incompatible import type")
+
+;; i64 (pagesize 1)
+(assert_unlinkable
+  (module
+    (import "test" "unknown" (memory i64 0xFFFF_FFFF_FFFF_FFFF (pagesize 1))))
+  "incompatible import type")
 
 ;; i64 (default pagesize)
 (assert_unlinkable
   (module
     (import "test" "unknown" (func))
     (memory i64 0x1_0000_0000_0000 (pagesize 65536)))
-  "unknown import")
+  "incompatible import type")
+
+;; i64 (default pagesize)
+(assert_unlinkable
+  (module
+    (import "test" "unknown" (memory i64 0x1_0000_0000_0000 (pagesize 65536))))
+  "incompatible import type")
 
 ;; Memory size just over the maximum.
 ;;
@@ -36,7 +48,7 @@
 ;; i64 (pagesize 1)
 (assert_malformed
   (module quote "(memory i64 0x1_0000_0000_0000_0000 (pagesize 1))")
-  "constant out of range")
+  "i64 constant out of range")
 
 ;; i64 (default pagesize)
 (assert_invalid