diff --git a/src/plasp/pddl/expressions/Not.cpp b/src/plasp/pddl/expressions/Not.cpp
index 72efe5b..0190d0b 100644
--- a/src/plasp/pddl/expressions/Not.cpp
+++ b/src/plasp/pddl/expressions/Not.cpp
@@ -52,7 +52,10 @@ ExpressionPointer Not::normalize()
 	{
 		auto &argument = dynamic_cast<Not &>(*m_argumentStorage);
 
-		return std::move(argument.m_argumentStorage);
+		auto normalized = std::move(argument.m_argumentStorage);
+		normalized->normalize();
+
+		return normalized;
 	}
 
 	auto normalizedArgument = m_argumentStorage->normalize();
diff --git a/tests/TestPDDLNormalization.cpp b/tests/TestPDDLNormalization.cpp
new file mode 100644
index 0000000..3b679ea
--- /dev/null
+++ b/tests/TestPDDLNormalization.cpp
@@ -0,0 +1,23 @@
+#include <gtest/gtest.h>
+
+#include <plasp/pddl/expressions/Not.h>
+#include <plasp/pddl/expressions/Unsupported.h>
+
+using namespace plasp::pddl;
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+TEST(PDDLNormalizationTests, DoubleNegation)
+{
+	auto n1 = std::make_unique<expressions::Not>();
+	auto n2 = std::make_unique<expressions::Not>();
+	auto u = std::make_unique<expressions::Unsupported>();
+	const auto up = u.get();
+
+	n2->setArgument(std::move(u));
+	n1->setArgument(std::move(n2));
+
+	auto normalized = n1->normalize();
+
+	ASSERT_EQ(normalized.get(), up);
+}