diff -ur kcalc-4.9.90/kcalc_core.cpp kcalc-4.9.90-misc/kcalc_core.cpp
--- kcalc-4.9.90/kcalc_core.cpp	2012-11-14 17:46:47.000000000 +0100
+++ kcalc-4.9.90-misc/kcalc_core.cpp	2012-12-08 20:05:58.000000000 +0100
@@ -99,7 +99,13 @@
 }
 
 KNumber ExecMod(const KNumber &left_op, const KNumber &right_op) {
-    return left_op % right_op;
+    KNumber tmp_result = left_op % right_op;
+
+    if ( right_op < KNumber::Zero )
+       return -(-left_op % -right_op);
+    if ( tmp_result < KNumber::Zero )
+       tmp_result += right_op;
+    return tmp_result;
 }
 
 KNumber ExecIntDiv(const KNumber &left_op, const KNumber &right_op) {
@@ -535,8 +541,11 @@
 
 void CalcEngine::Factorial(const KNumber &input)
 {
-    if (input == KNumber::PosInfinity) return;
-    if (input < KNumber::Zero || input.type() == KNumber::TYPE_ERROR) {
+    if (input == KNumber::PosInfinity || input > KNumber(999999)) {
+       last_number_ = KNumber::PosInfinity;
+       return;
+    }
+    if (input < KNumber::Zero || input.type() != KNumber::TYPE_INTEGER) {
         error_ = true;
         last_number_ = KNumber::NaN;
         return;