diff --git a/util.cpp b/util.cpp
index c48581d4..fdd51e1c 100644
--- a/util.cpp
+++ b/util.cpp
@@ -340,6 +340,8 @@ cld exp_parser::parse(int prio) {
     else if(number == "mousez") res = cld(mousex - current_display->xcenter, mousey - current_display->ycenter) / cld(current_display->radius, 0);
     else if(number == "shot") res = inHighQual ? 1 : 0;
     else if(number[0] >= 'a' && number[0] <= 'z') throw hr_parse_exception("unknown value: " + number);
+    else if(number[0] >= 'A' && number[0] <= 'Z') throw hr_parse_exception("unknown value: " + number);
+    else if(number[0] == '_') throw hr_parse_exception("unknown value: " + number);
     else { std::stringstream ss; res = 0; ss << number; ss >> res; }
     }
   while(true) {