diff --git a/src/c/reader.d b/src/c/reader.d
index 5f467f664..0efffe077 100644
--- a/src/c/reader.d
+++ b/src/c/reader.d
@@ -204,6 +204,32 @@ ecl_put_reader_token(cl_object token)
   the_env->token_pool = CONS(token, pool);
 }
 
+static ecl_character
+_ecl_string_push_extend(cl_object s, ecl_character c)
+{
+  cl_index dim, fillp;
+  switch(ecl_t_of(s)) {
+#ifdef ECL_UNICODE
+  case t_string:
+    fillp = s->string.fillp;
+    dim = s->string.dim;
+    if (fillp >= dim) {
+      ecl_internal_error("token is too long!");
+    }
+    return s->string.self[fillp++] = c;
+#endif
+  case t_base_string:
+    fillp = s->base_string.fillp;
+    dim = s->base_string.dim;
+    if (fillp >= dim) {
+      ecl_internal_error("token is too long!)");
+    }
+    return s->base_string.self[fillp++] = c;
+  default:
+    ecl_internal_error("can't do");
+  }
+}
+
 /*
  * This routine inverts the case of the characters in the buffer which were not
  * escaped.
@@ -255,7 +281,7 @@ ecl_read_token(cl_object rtbl, cl_object in, int flags)
     if (a == cat_single_escape) {
       c = ecl_read_char_noeof(in);
       a = cat_constituent;
-      ecl_string_push_extend(string, c);
+      _ecl_string_push_extend(string, c);
       length++;
       ecl_stack_push(escape, ecl_make_fixnum(length-1));
       ecl_stack_push(escape, ecl_make_fixnum(length));
@@ -271,7 +297,7 @@ ecl_read_token(cl_object rtbl, cl_object in, int flags)
           a = cat_constituent;
         } else if (a == cat_multiple_escape)
           break;
-        ecl_string_push_extend(string, c);
+        _ecl_string_push_extend(string, c);
         length++;
       }
       ecl_stack_push(escape, ecl_make_fixnum(begin));
@@ -298,7 +324,7 @@ ecl_read_token(cl_object rtbl, cl_object in, int flags)
           c = ecl_char_upcase(c);
       }
     }
-    ecl_string_push_extend(string, c);
+    _ecl_string_push_extend(string, c);
     length++;
   NEXT:
     c = ecl_read_char(in);