diff --git a/src/eval.c b/src/eval.c
index ecc242d..d0ad7c6 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -5087,7 +5087,8 @@
 		    ga_concat(&ga, tv2string(&dtv, &tf, numbuf, copyID));
 		    vim_free(tf);
 		}
-		ga_concat(&ga, (char_u *)")");
+		// terminate with ')' and a NUL
+		ga_concat_len(&ga, (char_u *)")", 2);
 
 		*tofree = ga.ga_data;
 		r = *tofree;