diff --git a/include/external/clara.h b/include/external/clara.h
index 6ab30136..0494745d 100644
--- a/include/external/clara.h
+++ b/include/external/clara.h
@@ -550,7 +550,7 @@ namespace Clara {
         }
 
         void parseIntoTokens( std::string const& arg, std::vector<Token>& tokens ) {
-            for( std::size_t i = 0; i <= arg.size(); ++i ) {
+            for( std::size_t i = 0; i < arg.size(); ++i ) {
                 char c = arg[i];
                 if( c == '"' )
                     inQuotes = !inQuotes;