diff --git a/ext/mini_racer_extension/mini_racer_extension.c b/ext/mini_racer_extension/mini_racer_extension.c
index 12a27ff..42aecce 100644
--- a/ext/mini_racer_extension/mini_racer_extension.c
+++ b/ext/mini_racer_extension/mini_racer_extension.c
@@ -171,13 +171,14 @@ static void *rendezvous_callback(void *arg);
 typedef struct State
 {
     VALUE   a, b;
+    uint8_t verbatim_keys:1;
 } State;
 
 // note: must be stack-allocated or VALUEs won't be visible to ruby's GC
 typedef struct DesCtx
 {
     State   *tos;
-    VALUE   refs; // array
+    VALUE   refs; // object refs array
     uint8_t transcode_latin1:1;
     char    err[64];
     State   stack[512];
@@ -199,7 +200,7 @@ static void DesCtx_init(DesCtx *c)
 {
     c->tos  = c->stack;
     c->refs = rb_ary_new();
-    *c->tos = (State){Qundef, Qundef};
+    *c->tos = (State){Qundef, Qundef, /*verbatim_keys*/0};
     *c->err = '\0';
     c->transcode_latin1 = 1; // convert to utf8
 }
@@ -220,7 +221,8 @@ static void put(DesCtx *c, VALUE v)
         if (*b == Qundef) {
             *b = v;
         } else {
-            *b = rb_funcall(*b, rb_intern("to_s"), 0);
+            if (!c->tos->verbatim_keys)
+                *b = rb_funcall(*b, rb_intern("to_s"), 0);
             rb_hash_aset(*a, *b, v);
             *b = Qundef;
         }
@@ -242,7 +244,7 @@ static void push(DesCtx *c, VALUE v)
         snprintf(c->err, sizeof(c->err), "stack overflow");
         return;
     }
-    *++c->tos = (State){v, Qundef};
+    *++c->tos = (State){v, Qundef, /*verbatim_keys*/0};
     rb_ary_push(c->refs, v);
 }
 
@@ -426,6 +428,20 @@ static void des_object_end(void *arg)
     pop(arg);
 }
 
+static void des_map_begin(void *arg)
+{
+    DesCtx *c;
+
+    c = arg;
+    push(c, rb_hash_new());
+    c->tos->verbatim_keys = 1; // don't stringify or intern keys
+}
+
+static void des_map_end(void *arg)
+{
+    pop(arg);
+}
+
 static void des_object_ref(void *arg, uint32_t id)
 {
     DesCtx *c;
diff --git a/ext/mini_racer_extension/serde.c b/ext/mini_racer_extension/serde.c
index 3c51ce2..65aab21 100644
--- a/ext/mini_racer_extension/serde.c
+++ b/ext/mini_racer_extension/serde.c
@@ -31,6 +31,8 @@ static void des_named_props_begin(void *arg);
 static void des_named_props_end(void *arg);
 static void des_object_begin(void *arg);
 static void des_object_end(void *arg);
+static void des_map_begin(void *arg);
+static void des_map_end(void *arg);
 static void des_object_ref(void *arg, uint32_t id);
 // des_error_begin: followed by des_object_begin + des_object_end calls
 static void des_error_begin(void *arg);
@@ -642,7 +644,7 @@ static int des1(char (*err)[64], const uint8_t **p, const uint8_t *pe,
         des_object_end(arg);
         break;
     case ';': // Map
-        des_object_begin(arg);
+        des_map_begin(arg);
         for (u = 0; /*empty*/; u++) {
             if (*p >= pe)
                 goto too_short;
@@ -658,7 +660,7 @@ static int des1(char (*err)[64], const uint8_t **p, const uint8_t *pe,
             goto bad_varint;
         if (t != 2*u)
             return bail(err, "map element count mismatch");
-        des_object_end(arg);
+        des_map_end(arg);
         break;
     case '\'': // Set
         des_array_begin(arg);
diff --git a/test/mini_racer_test.rb b/test/mini_racer_test.rb
index 5e2d8b9..2a894c8 100644
--- a/test/mini_racer_test.rb
+++ b/test/mini_racer_test.rb
@@ -1097,7 +1097,7 @@ def test_function_property
       }
     else
       expected = {
-        "m" => {"1" => 2, "3" => 4}, # TODO(bnoordhuis) retain numeric keys
+        "m" => {1 => 2, 3 => 4},
         "s" => [5, 7, 11, 13],
         "x" => 42,
       }