diff --git a/kcalc.cpp b/kcalc.cpp
--- a/kcalc.cpp
+++ b/kcalc.cpp
@@ -1543,17 +1543,14 @@
 	if(KCalcConstButton *btn = qobject_cast<KCalcConstButton*>(const_buttons_[button])) {
 		if (!shift_mode_) {
 			// set the display to the configured value of constant button
-			// internally, we deal with C locale style numbers, we need to convert
 			QString val = btn->constant();
-			val.replace(QLatin1Char('.'), KNumber::decimalSeparator());
+			if (KCalcSettings::groupDigits() && !(QLocale().numberOptions() & QLocale::OmitGroupSeparator))
+				val.remove(KNumber::groupSeparator());
 			calc_display->setAmount(KNumber(val));
-
 		} else {
 			pbShift->setChecked(false);
 
-			// internally, we deal with C locale style numbers, we need to convert
 			QString val = calc_display->text();
-			val.replace(KNumber::decimalSeparator(), QLatin1String("."));
 			KCalcSettings::setValueConstant(button, val);
 
 			// below set new tooltip