diff --git a/src/emacs-module.c b/src/emacs-module.c
index 0abfd3f6f1..4f2b0ecd4b 100644
--- a/src/emacs-module.c
+++ b/src/emacs-module.c
@@ -458,6 +458,8 @@ module_make_function (emacs_env *env, ptrdiff_t min_arity, ptrdiff_t max_arity,
   return lisp_to_value (env, result);
 }
 
+static bool my_check = false;
+
 static emacs_value
 module_funcall (emacs_env *env, emacs_value fun, ptrdiff_t nargs,
 		emacs_value args[])
@@ -473,6 +475,7 @@ module_funcall (emacs_env *env, emacs_value fun, ptrdiff_t nargs,
     xsignal0 (Qoverflow_error);
   SAFE_ALLOCA_LISP (newargs, nargs1);
   newargs[0] = value_to_lisp (fun);
+  my_check = EQ (newargs[0], Qfile_name_as_directory);
   for (ptrdiff_t i = 0; i < nargs; i++)
     newargs[1 + i] = value_to_lisp (args[i]);
   emacs_value result = lisp_to_value (env, Ffuncall (nargs1, newargs));
@@ -581,8 +584,10 @@ module_make_string (emacs_env *env, const char *str, ptrdiff_t length)
   /* FIXME: AUTO_STRING_WITH_LEN requires STR to be null-terminated,
      but we shouldn't require that.  */
   AUTO_STRING_WITH_LEN (lstr, str, length);
-  return lisp_to_value (env,
-                        code_convert_string_norecord (lstr, Qutf_8, false));
+  Lisp_Object lisp = code_convert_string_norecord (lstr, Qutf_8, false);
+  eassert (STRINGP (lisp) && SSDATA (lisp));
+  my_check = true;
+  return lisp_to_value (env, lisp);
 }
 
 static emacs_value
@@ -955,6 +960,8 @@ value_to_lisp_bits (emacs_value v)
 static Lisp_Object
 value_to_lisp (emacs_value v)
 {
+  bool b = my_check;
+  my_check = false;
   if (module_assertions)
     {
       /* Check the liveness of the value by iterating over all live
@@ -972,7 +979,11 @@ value_to_lisp (emacs_value v)
             {
               Lisp_Object *p = XSAVE_POINTER (XCAR (values), 0);
               if (p == optr)
-                return *p;
+                {
+                  if (b)
+                    eassert (STRINGP (*p) && SSDATA (*p));
+                  return *p;
+                }
               ++num_values;
             }
           ++num_environments;
@@ -1008,6 +1019,8 @@ lisp_to_value_bits (Lisp_Object o)
 static emacs_value
 lisp_to_value (emacs_env *env, Lisp_Object o)
 {
+  bool b = my_check;
+  my_check = false;
   if (module_assertions)
     {
       /* Add the new value to the list of values allocated from this
@@ -1020,6 +1033,11 @@ lisp_to_value (emacs_env *env, Lisp_Object o)
       ATTRIBUTE_MAY_ALIAS emacs_value ret = vptr;
       struct emacs_env_private *priv = env->private_members;
       priv->values = Fcons (make_save_ptr (ret), priv->values);
+      if (b)
+        {
+          eassert (STRINGP (o) && SSDATA (o));
+          eassert (STRINGP (*optr) && SSDATA (*optr));
+        }
       return ret;
     }