diff --git a/src_main/math/pievaluator.cpp b/src_main/math/pievaluator.cpp
index 0c74a6ae..96da7e21 100755
--- a/src_main/math/pievaluator.cpp
+++ b/src_main/math/pievaluator.cpp
@@ -1039,9 +1039,7 @@ inline void PIEvaluator::execFunction(const Instruction & ci) {
 		tmpvars[oi].value = atanc(value(ci.operators[0]));
 		break;
 	case bfArcctg:
-		tmp = atanc(value(ci.operators[0]));
-		if (tmp == complexd_0) tmpvars[oi].value = 0.;
-		else tmpvars[oi].value = complexd_1 / tmp;
+		tmpvars[oi].value = atanc(-value(ci.operators[0])) + M_PI_2;
 		break;
 	case bfSh:
 		tmpvars[oi].value = sinh(value(ci.operators[0]));