diff --git a/src/evalfunc.c b/src/evalfunc.c
index 57c4ffb..afc8977 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -2436,6 +2436,12 @@
     expand_T	xpc;
     int		error = FALSE;
     char_u	*result;
+#ifdef BACKSLASH_IN_FILENAME
+    char_u	*p_csl_save = p_csl;
+
+    // avoid using 'completeslash' here
+    p_csl = empty_option;
+#endif
 
     rettv->v_type = VAR_STRING;
     if (argvars[1].v_type != VAR_UNKNOWN
@@ -2488,6 +2494,9 @@
 	else
 	    rettv->vval.v_string = NULL;
     }
+#ifdef BACKSLASH_IN_FILENAME
+    p_csl = p_csl_save;
+#endif
 }
 
 /*