diff --git a/src/libslic3r/PrintConfig.cpp b/src/libslic3r/PrintConfig.cpp
index 7099c9aeb..8d0333a6e 100644
--- a/src/libslic3r/PrintConfig.cpp
+++ b/src/libslic3r/PrintConfig.cpp
@@ -4488,6 +4488,9 @@ void PrintConfigDef::handle_legacy(t_config_option_key &opt_key, std::string &va
         float v = boost::lexical_cast<float>(value);
         if (v > 0)
             value = boost::lexical_cast<std::string>(-v);
+    } else if (opt_key == "thumbnails") {
+        if (value.empty())
+            value = "0x0,0x0";
     } else if (opt_key == "z_steps_per_mm") {
         opt_key = "z_step";
         float v = boost::lexical_cast<float>(value);