diff --git a/src/util.cpp b/src/util.cpp
index 38027855..31fa186c 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -59,7 +59,7 @@ std::string quoteIfNeeded (const std::string& input)
 
   auto quote = input.find ('"');
   auto space = input.find (' ');
-  auto op    = input.find_first_of ("+-/()<^!=~_");
+  auto op    = input.find_first_of ("+-/()<^!=~_%");
 
   if (quote == std::string::npos &&
       space == std::string::npos &&