diff --git a/treesource.c b/treesource.c
index 2acb920..061ba8c 100644
--- a/treesource.c
+++ b/treesource.c
@@ -183,7 +183,7 @@ static enum markertype guess_value_type(struct property *prop)
 			nnotcelllbl++;
 	}
 
-	if ((p[len-1] == '\0') && (nnotstring == 0) && (nnul < (len-nnul))
+	if ((p[len-1] == '\0') && (nnotstring == 0) && (nnul <= (len-nnul))
 	    && (nnotstringlbl == 0)) {
 		return TYPE_STRING;
 	} else if (((len % sizeof(cell_t)) == 0) && (nnotcelllbl == 0)) {