diff --git a/libs/main/math/pievaluator.cpp b/libs/main/math/pievaluator.cpp
index 87414136..ebd42eed 100644
--- a/libs/main/math/pievaluator.cpp
+++ b/libs/main/math/pievaluator.cpp
@@ -343,6 +343,9 @@ void PIEvaluator::findUnknownVariables() {
 	if (cvar.length() > 0) unknownVars << cvar;
 	unknownVars.removeDuplicates();
 	usedVars.removeDuplicates();
+	usedVars.removeOne("i");
+	usedVars.removeOne("pi");
+	usedVars.removeOne("e");
 }