diff --git a/src/json.c b/src/json.c
index 928825e034..033fa27638 100644
--- a/src/json.c
+++ b/src/json.c
@@ -225,8 +225,17 @@ json_has_suffix (const char *string, const char *suffix)
 static Lisp_Object
 json_make_string (const char *data, ptrdiff_t size)
 {
-  return code_convert_string (make_specified_string (data, -1, size, false),
-                              Qutf_8_unix, Qt, false, true, true);
+  ptrdiff_t nchars, multibyte_nbytes;
+  parse_str_as_multibyte ((const unsigned char *) data, size,
+                          &nchars, &multibyte_nbytes);
+
+  if (size == nchars)
+    /* Wasn't sure if the last arg should better be true here, but
+       it doesn't seem to affect the behavior or correctness, so far. */
+    return make_specified_string (data, -1, size, false);
+  else
+    return code_convert_string (make_specified_string (data, -1, size, false),
+                                Qutf_8_unix, Qt, false, true, true);
 }
 
 /* Create a multibyte Lisp string from the NUL-terminated UTF-8