diff --git a/src/keys.cc b/src/keys.cc
index e624767c..edbd5e0c 100644
--- a/src/keys.cc
+++ b/src/keys.cc
@@ -126,7 +126,7 @@ KeyList parse_keys(StringView str)
             result.push_back(canonicalize_ifn({ modifier, name_it->key }));
         else if (desc.char_length() == 1)
             result.push_back(canonicalize_ifn({ modifier, desc[0_char] }));
-        else if (to_lower(desc[0_byte]) == 'f' and desc.length() <= 3)
+        else if (desc[0_byte] == 'F' and desc.length() <= 3)
         {
             int val = str_to_int(desc.substr(1_byte));
             if (val >= 1 and val <= 12)