diff --git a/search/search_quality/assessment_tool/edits.cpp b/search/search_quality/assessment_tool/edits.cpp
index 24bd33a5f3..47dbfcad11 100644
--- a/search/search_quality/assessment_tool/edits.cpp
+++ b/search/search_quality/assessment_tool/edits.cpp
@@ -7,7 +7,10 @@ namespace
 void UpdateNumEdits(Edits::Entry const & entry, Edits::MaybeRelevance const & r, size_t & numEdits)
 {
   if (entry.m_curr != entry.m_orig && r == entry.m_orig)
+  {
+    CHECK_GREATER(numEdits, 0, ());
     --numEdits;
+  }
   if (entry.m_curr == entry.m_orig && r != entry.m_orig)
     ++numEdits;
 }