diff -pruN mozc-2.23.2815.102.orig/prediction/zero_query_dict.h mozc-2.23.2815.102/prediction/zero_query_dict.h
--- mozc-2.23.2815.102.orig/prediction/zero_query_dict.h	2018-01-26 18:48:12.000000000 +0900
+++ mozc-2.23.2815.102/prediction/zero_query_dict.h	2018-06-01 16:08:24.548653648 +0900
@@ -147,6 +147,17 @@ class ZeroQueryDict {
       return iter;
     }
 
+    iterator &operator--() {
+      ptr_ -= kTokenByteSize;
+      return *this;
+    }
+
+    iterator operator--(int) {
+      const iterator tmp(ptr_, string_array_);
+      ptr_ -= kTokenByteSize;
+      return tmp;
+    }
+
     iterator &operator-=(ptrdiff_t n) {
       ptr_ -= n * kTokenByteSize;
       return *this;