diff --git a/ZString.cpp b/ZString.cpp
index 59f3467..0d3f460 100644
--- a/ZString.cpp
+++ b/ZString.cpp
@@ -370,6 +370,22 @@ namespace coreutils {
    }
 
    ZString &ZString::operator[](int index) {
+      // Previously an unchecked std::vector index - a single
+      // malformed/short line (a port scanner, a bot probing the port,
+      // or any client sending fewer colon-delimited fields than a
+      // given handler indexes) reaches every command handler across
+      // every server built on this class via request[N] with no
+      // length check first. Depending on build flags that was either
+      // undefined behavior or - confirmed live, crashing a real game
+      // server - a hard process abort (libstdc++'s own vector bounds
+      // assertion). Throwing here instead lets it be caught: every
+      // caller that dispatches a parsed request already wraps that
+      // dispatch in a try/catch (see CommandList::processRequest()),
+      // so this turns "one bad line takes down the whole server" into
+      // "that one line is cleanly rejected."
+      if (index < 0 || (size_t)index >= list.size())
+         throw coreutils::Exception("ZString::operator[]: index " + std::to_string(index) +
+                                     " out of range (have " + std::to_string(list.size()) + ")");
       return list[index];
    }