diff --git a/src/makernote.cpp b/src/makernote.cpp
index 034882d7..c4f3a203 100644
--- a/src/makernote.cpp
+++ b/src/makernote.cpp
@@ -86,6 +86,7 @@ namespace Exiv2 {
     bool TiffMnRegistry::operator==(const std::string& key) const
     {
         std::string make(make_);
+        if (key.size() > 0 && key[0] == '-') return false;
         return make == key.substr(0, make.length());
     }