diff --git a/src/core/config.h b/src/core/config.h
index b567b0699..c919ccd10 100644
--- a/src/core/config.h
+++ b/src/core/config.h
@@ -64,7 +64,7 @@ inline std::string u16to8(const std::wstring& u16) {
 
 static inline size_t u8cols(const std::string& str) {
     std::wstring wstr = u8to16(str);
-    return (size_t) std::max(0, wcswidth(wstr.c_str(), str.size()));
+    return (size_t) std::max(0, wcswidth(wstr.c_str(), wstr.size()));
 }
 
 inline static size_t u8len(const std::string& str) {