Don't access invalid string indexes

1 files changed, 2 insertions, 2 deletions

diff --git a/apt-pkg/deb/debmetaindex.cc b/apt-pkg/deb/debmetaindex.cc
index f25906fba..610965024 100644
--- a/apt-pkg/deb/debmetaindex.cc
+++ b/apt-pkg/deb/debmetaindex.cc
@@ -682,13 +682,13 @@ bool debReleaseIndex::SetSignedBy(std::string const &pSignedBy)
 	 SignedBy = os.str();
       }
       // Normalize the string: Remove trailing commas
-      while (SignedBy[SignedBy.size() - 1] == ',')
+      while (SignedBy.size() > 0 && SignedBy[SignedBy.size() - 1] == ',')
 	 SignedBy.resize(SignedBy.size() - 1);
    }
    else {
       // Only compare normalized strings
       auto pSignedByView = APT::StringView(pSignedBy);
-      while (pSignedByView[pSignedByView.size() - 1] == ',')
+      while (pSignedByView.size() > 0 && pSignedByView[pSignedByView.size() - 1] == ',')
 	 pSignedByView = pSignedByView.substr(0, pSignedByView.size() - 1);
       if (pSignedByView != SignedBy)
 	 return _error->Error(_("Conflicting values set for option %s regarding source %s %s: %s != %s"), "Signed-By", URI.c_str(), Dist.c_str(), SignedBy.c_str(), pSignedByView.to_string().c_str());