diff --git a/ml-proto/host/builtins.ml b/ml-proto/host/builtins.ml
index fa599e7987..dfa6eaa39a 100644
--- a/ml-proto/host/builtins.ml
+++ b/ml-proto/host/builtins.ml
@@ -1,9 +1,50 @@
 open Source
+open Eval
+open Memory
+open Types
 
-let print vs =
+let print m vs =
   List.iter Print.print_value (List.map (fun v -> Some v) vs);
   None
 
+let rec stdout_write_inner at mem offset count i =
+  let load_result = Memory.load_extend mem (Int64.add offset i) Mem8 ZX Int32Type in
+
+  begin
+    match load_result with
+    | Values.Int32 byte ->
+      print_char (Char.chr (Int32.to_int byte))
+    | _ ->
+      ignore (Error.error at "load_extend returned wrong type")
+  end;
+
+  let next = Int64.succ i in
+  let should_iterate = (Int64.compare next count) < 0 in
+
+  if should_iterate then
+    ignore (stdout_write_inner at mem offset count next)
+  else
+    ();
+
+and stdout_write at m vs =
+  if List.length vs != 2 then
+    Error.error at "stdio.write expects 2 arguments (offset, count)";
+
+  let mem = Eval.memory_for_module at m in
+  match vs with
+  | [Values.Int32 _offset; Values.Int32 _count] ->
+    let offset = (Int64.of_int32 _offset) in
+    let count  = (Int64.of_int32 _count) in
+
+    set_binary_mode_out stdout false;
+    ignore (stdout_write_inner at mem offset count Int64.zero);
+    set_binary_mode_out stdout true;
+    None
+
+  | _ -> 
+    ignore (Error.error at "stdio.write expected i32 offset, i32 count");
+    None
+
 let match_import i =
   let {Ast.module_name; func_name; func_params; func_result} = i.it in
   if module_name <> "stdio" then
@@ -13,6 +54,10 @@ let match_import i =
     if func_result <> None then
       Error.error i.at "stdio.print has no result";
     print
+  | "write" ->
+    if func_result <> None then
+      Error.error i.at "stdio.write has no result";  
+    stdout_write i.at
   | _ ->
     Error.error i.at ("no stdio." ^ func_name ^ "\"")
 
diff --git a/ml-proto/spec/eval.ml b/ml-proto/spec/eval.ml
index 121d5fa51a..e5fef35362 100644
--- a/ml-proto/spec/eval.ml
+++ b/ml-proto/spec/eval.ml
@@ -13,13 +13,13 @@ let error = Error.error
 
 type value = Values.value
 type func = Ast.func
-type import = value list -> value option
 type host_params = {page_size : Memory.size}
 
 module ExportMap = Map.Make(String)
 type export_map = func ExportMap.t
 
-type instance =
+type import = instance -> value list -> value option
+and  instance =
 {
   funcs : func list;
   imports : import list;
@@ -159,7 +159,7 @@ let rec eval_expr (c : config) (e : expr) =
 
   | CallImport (x, es) ->
     let vs = List.map (fun ev -> some (eval_expr c ev) ev.at) es in
-    (import c x) vs
+    (import c x) c.module_ vs
 
   | CallIndirect (x, e1, es) ->
     let i = int32 (eval_expr c e1) e1.at in
@@ -312,3 +312,10 @@ let host_eval e =
   let host = {page_size = 1L} in
   let m = {imports = []; exports; tables = []; funcs = [f]; memory = None; host} in
   eval_func m f []
+
+let memory_for_module at m =
+  match m.memory with
+  | Some mem ->
+    mem
+  | _ ->
+    error at "Module has no memory";
diff --git a/ml-proto/spec/eval.mli b/ml-proto/spec/eval.mli
index 2442bfe13f..91b207dec7 100644
--- a/ml-proto/spec/eval.mli
+++ b/ml-proto/spec/eval.mli
@@ -4,12 +4,13 @@
 
 type instance
 type value = Values.value
-type import = value list -> value option
+type import = instance -> value list -> value option
 type host_params = {page_size : Memory.size}
 
 val init : Ast.module_ -> import list -> host_params -> instance
 val invoke : instance -> string -> value list -> value option
   (* raise Error.Error *)
 
-(* This function is not part of the spec. *)
+(* These functions are not part of the spec. *)
 val host_eval : Ast.expr -> value option (* raise Error.Error *)
+val memory_for_module : Source.region -> instance -> Memory.t
\ No newline at end of file
diff --git a/ml-proto/test/expected-output/stdio_write.wast.log b/ml-proto/test/expected-output/stdio_write.wast.log
new file mode 100644
index 0000000000..aa860abb47
Binary files /dev/null and b/ml-proto/test/expected-output/stdio_write.wast.log differ
diff --git a/ml-proto/test/stdio_write.wast b/ml-proto/test/stdio_write.wast
new file mode 100644
index 0000000000..80eae6fbd2
--- /dev/null
+++ b/ml-proto/test/stdio_write.wast
@@ -0,0 +1,13 @@
+(module 
+  (import $write "stdio" "write" (param i32 i32))
+
+  (memory 4096 4096 (segment 0 "\89\50\4e\47\0d\0a\1a\0a\00"))
+
+  (func $write_png_header
+    (call_import $write (i32.const 0) (i32.const 9))
+  )
+
+  (export "write_png_header" $write_png_header)
+)
+
+(invoke "write_png_header")
\ No newline at end of file