diff --git a/src/core/wee-hashtable.c b/src/core/wee-hashtable.c
index 57c9c510f..f33db8c25 100644
--- a/src/core/wee-hashtable.c
+++ b/src/core/wee-hashtable.c
@@ -554,7 +554,7 @@ hashtable_compute_length_values_cb (void *data,
     }
     else
     {
-        *length += strlen ("(null)");
+        *length += strlen ("(null)") + 1;
     }
 }