diff --git a/.vscode/launch.json b/.vscode/launch.json
index 4d023ae..c865479 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -10,7 +10,7 @@
             "request": "launch",
             "program": "${workspaceRoot}/sample/build/sample",
             "args": [
-                "test"
+                "mfeat-factors"
             ],
             "stopAtEntry": false,
             "cwd": "${workspaceRoot}/sample/build/",
diff --git a/CPPFImdlp.cpp b/CPPFImdlp.cpp
index 59b9b4b..1c6234f 100644
--- a/CPPFImdlp.cpp
+++ b/CPPFImdlp.cpp
@@ -32,10 +32,12 @@ namespace mdlp {
 
     pair<precision_t, size_t> CPPFImdlp::valueCutPoint(size_t start, size_t cut, size_t end)
     {
-        size_t n, m, idxPrev = cut - 1 <= start ? cut - 1 : cut;
+        size_t n, m, idxPrev = cut - 1 >= start ? cut - 1 : cut;
         size_t idxNext = cut + 1 < end ? cut + 1 : cut;
         bool backWall; // true if duplicates reach begining of the interval
         precision_t previous, actual, next;
+        if (cut - 1 < start || cut + 1 >= end)
+            throw logic_error("Invalid cutpoint index");
         previous = X[indices[idxPrev]];
         actual = X[indices[cut]];
         next = X[indices[idxNext]];