diff --git a/rtgui/main-cli.cc b/rtgui/main-cli.cc
index 347161cd5..26ee4fa81 100644
--- a/rtgui/main-cli.cc
+++ b/rtgui/main-cli.cc
@@ -280,7 +280,7 @@ int processLineParams ( int argc, char **argv )
         currParam = currParam.substr (1, currParam.length() - 2);
 #endif
 
-        if ( currParam.at (0) == '-' ) {
+        if ( currParam.at (0) == '-' && currParam.size() > 1) {
             switch ( currParam.at (1) ) {
                 case 'O':
                     copyParamsFile = true;