diff -ur ebook-tools-0.2.2.0/src/libepub/linklist.c ebook-tools-0.2.2/src/libepub/linklist.c
--- ebook-tools-0.2.2.0/src/libepub/linklist.c	2012-09-04 07:32:32.000000000 -0700
+++ ebook-tools-0.2.2/src/libepub/linklist.c	2019-09-19 17:38:55.499059141 -0700
@@ -115,7 +115,8 @@
       
       while ((Compare = (List->compare)(List->Current->Data, Data)) != 0) {
 		  List->Current = List->Current->Next;
-		  if (List->Current == NULL)
+		  if ((List->Current == NULL) ||
+		      (List->Current->Data == NULL))
 			  return NULL; // end of list
 	  }
     }
diff -ur ebook-tools-0.2.2.0/src/libepub/list.c ebook-tools-0.2.2/src/libepub/list.c
--- ebook-tools-0.2.2.0/src/libepub/list.c	2012-09-04 07:32:32.000000000 -0700
+++ ebook-tools-0.2.2/src/libepub/list.c	2019-09-19 17:33:49.780068574 -0700
@@ -137,6 +137,9 @@
 
 int _list_cmp_label_by_lang(struct tocLabel *t1, struct tocLabel *t2) {
 
+  if ((t1 == NULL) || (t2 == NULL))
+    return 0;
+
   if (! t1->lang || ! t2->lang)
     return 0;