diff --git a/alib2data/src/automaton/PDA/VisiblyPushdownNPDA.cpp b/alib2data/src/automaton/PDA/VisiblyPushdownNPDA.cpp
index 8e30cb35cf68e9259fac7534c8cc2ab7ae3f4fd4..61b6cf21116828c8145ed7e6a06f956432e74953 100644
--- a/alib2data/src/automaton/PDA/VisiblyPushdownNPDA.cpp
+++ b/alib2data/src/automaton/PDA/VisiblyPushdownNPDA.cpp
@@ -134,7 +134,7 @@ bool VisiblyPushdownNPDA::addTransition(const State& from, const alphabet::Symbo
 		throw AutomatonException("State \"" + (std::string) from.getName() + "\" doesn't exist.");
 	}
 
-	if (callInputAlphabet.find(input) == callInputAlphabet.end()) {
+	if (returnInputAlphabet.find(input) == returnInputAlphabet.end()) {
 		throw AutomatonException("Input symbol \"" + (std::string) input + "\" doesn't exist.");
 	}
 
@@ -156,7 +156,7 @@ bool VisiblyPushdownNPDA::addTransition(const State& from, const alphabet::Symbo
 		throw AutomatonException("State \"" + (std::string) from.getName() + "\" doesn't exist.");
 	}
 
-	if (callInputAlphabet.find(input) == callInputAlphabet.end()) {
+	if (localInputAlphabet.find(input) == localInputAlphabet.end()) {
 		throw AutomatonException("Input symbol \"" + (std::string) input + "\" doesn't exist.");
 	}