diff --git a/filecomplete.cpp b/filecomplete.cpp
index 4ed3e9f..4727ac5 100644
--- a/filecomplete.cpp
+++ b/filecomplete.cpp
@@ -590,7 +590,10 @@ void add_newer(const std::vector<char>& wch)
             buf.resize(buf.size() * 2);
         }
         if (len > 0) {
-            for (size_t i = len - 1; i >= wo; --i) {
+            for (int i = len - 1; i >= wo; --i) {
+                if (i < 0) {
+                    break;
+                }
                 buf[i + 1] = buf[i];
             }
         }