diff --git a/src/collocatordb.cc b/src/collocatordb.cc
index 4da2e06..6eda410 100644
--- a/src/collocatordb.cc
+++ b/src/collocatordb.cc
@@ -859,7 +859,12 @@
   /* fixed size, so it lives on the stack and cannot be leaked */
   uint64_t sumWindow[2 * WINDOW_SIZE];
   memset(sumWindow, 0, sizeof(sumWindow));
-  int true_window_size = 1;
+  /* Counted up from zero, since the first key of the iteration takes the same
+     branch as any further key of the same collocate, which increments it. It
+     used to start at one, so that the first collocate of every query was scored
+     with a window one position too wide, which inflated its expected frequency
+     and thus lowered its pmi, npmi, md, lfmd and llr. */
+  int true_window_size = 0;
   int usedPositions = 0;
 
   if (w1 > _vocab.size()) {