diff --git a/src/fns.c b/src/fns.c
index aba34fd2611..de1dad3736e 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -4952,6 +4952,9 @@ extract_data_from_object (Lisp_Object spec,
 #endif
     }
 
+  if (!STRINGP (object))
+    signal_error ("Invalid object argument",
+		  NILP (object) ? build_string ("nil") : object);
   return SSDATA (object);
 }