diff --git a/test.cpp b/test.cpp
index 9c3cc0f..d491143 100644
--- a/test.cpp
+++ b/test.cpp
@@ -133,8 +133,8 @@ protected:
   }
 
   double rate(Mapping const &m, int max_order = -1) const {
-    const auto order =
-        (-1 == max_order) ? corpus.order() : static_cast<size_t>(max_order);
+    const auto order = 1 + ((-1 == max_order) ? corpus.order()
+                                              : static_cast<size_t>(max_order));
     double score = 0.;
     char map[256];
     m.create_map(&map[0]);
@@ -143,14 +143,13 @@ protected:
     for (size_t i = 0, valid = 0; i < len; i++) {
       if (plain_text[i]) {
         valid++;
-        if (valid == (order + 1)) {
-          score += log(corpus.probability(&plain_text[i - valid], valid));
-        } else if (valid > (order + 1)) {
-          score += log(
-              corpus.final_probability(&plain_text[i - order - 1], order + 1));
+        if (valid == order) {
+          score += log(corpus.probability(&plain_text[i - order], order));
+        } else if (valid > order) {
+          score += log(corpus.final_probability(&plain_text[i - order], order));
         }
       } else {
-        if (valid && (valid <= order)) {
+        if (valid && (valid < order)) {
           score += log(corpus.probability(&plain_text[i - valid], valid));
         }
         valid = 0;