diff --git a/include/plasp/utils/IO.h b/include/plasp/utils/IO.h
index d2d022e..f16ddd5 100644
--- a/include/plasp/utils/IO.h
+++ b/include/plasp/utils/IO.h
@@ -40,6 +40,18 @@ inline std::string unescapeASP(const std::string &string)
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
+inline std::string toLowerCase(const std::string &string)
+{
+	std::string result;
+	result.resize(string.size());
+
+	std::transform(string.begin(), string.end(), result.begin(), ::tolower);
+
+	return result;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
 }
 }
 
diff --git a/src/plasp/pddl/Domain.cpp b/src/plasp/pddl/Domain.cpp
index 4c0002e..77dfd5a 100644
--- a/src/plasp/pddl/Domain.cpp
+++ b/src/plasp/pddl/Domain.cpp
@@ -8,6 +8,7 @@
 #include <plasp/pddl/expressions/PredicateDeclaration.h>
 #include <plasp/pddl/expressions/PrimitiveType.h>
 #include <plasp/pddl/expressions/Variable.h>
+#include <plasp/utils/IO.h>
 #include <plasp/utils/ParserException.h>
 
 namespace plasp
@@ -104,7 +105,7 @@ void Domain::parseSection()
 	m_context.parser.expect<std::string>("(");
 	m_context.parser.expect<std::string>(":");
 
-	const auto sectionIdentifier = m_context.parser.parseIdentifier(isIdentifier);
+	const auto sectionIdentifier = utils::toLowerCase(m_context.parser.parseIdentifier(isIdentifier));
 
 	const auto skipSection =
 		[&]()
@@ -149,6 +150,8 @@ void Domain::parseSection()
 		skipSection();
 	else if (sectionIdentifier == "derived")
 		skipSection();
+	else
+		throw utils::ParserException(m_context.parser, "Unknown domain section \"" + sectionIdentifier + "\"");
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/src/plasp/pddl/Expression.cpp b/src/plasp/pddl/Expression.cpp
index eb4cba6..987ccd0 100644
--- a/src/plasp/pddl/Expression.cpp
+++ b/src/plasp/pddl/Expression.cpp
@@ -9,6 +9,7 @@
 #include <plasp/pddl/expressions/Predicate.h>
 #include <plasp/pddl/expressions/PredicateDeclaration.h>
 #include <plasp/pddl/expressions/Reference.h>
+#include <plasp/utils/IO.h>
 #include <plasp/utils/ParserException.h>
 
 namespace plasp
@@ -42,7 +43,7 @@ ExpressionPointer parsePreconditionExpression(Context &context,
 {
 	context.parser.expect<std::string>("(");
 
-	const auto expressionIdentifier = context.parser.parseIdentifier(isIdentifier);
+	const auto expressionIdentifier = utils::toLowerCase(context.parser.parseIdentifier(isIdentifier));
 
 	ExpressionPointer expression;
 
@@ -70,7 +71,7 @@ ExpressionPointer parseExpression(Context &context, const expressions::Variables
 {
 	context.parser.expect<std::string>("(");
 
-	const auto expressionIdentifier = context.parser.parseIdentifier(isIdentifier);
+	const auto expressionIdentifier = utils::toLowerCase(context.parser.parseIdentifier(isIdentifier));
 
 	auto expression = parseExpressionContent(expressionIdentifier, context, parameters);
 
@@ -137,7 +138,7 @@ ExpressionPointer parseEffectExpression(Context &context, const expressions::Var
 {
 	context.parser.expect<std::string>("(");
 
-	const auto expressionIdentifier = context.parser.parseIdentifier(isIdentifier);
+	const auto expressionIdentifier = utils::toLowerCase(context.parser.parseIdentifier(isIdentifier));
 
 	ExpressionPointer expression;
 
diff --git a/src/plasp/pddl/Requirement.cpp b/src/plasp/pddl/Requirement.cpp
index e4f0ed0..834fc86 100644
--- a/src/plasp/pddl/Requirement.cpp
+++ b/src/plasp/pddl/Requirement.cpp
@@ -5,6 +5,7 @@
 #include <boost/bimap.hpp>
 
 #include <plasp/pddl/Identifier.h>
+#include <plasp/utils/IO.h>
 #include <plasp/utils/ParserException.h>
 
 namespace plasp
@@ -81,7 +82,7 @@ Requirement::Requirement(Requirement::Type type)
 
 Requirement Requirement::parse(Context &context)
 {
-	const auto requirementName = context.parser.parseIdentifier(isIdentifier);
+	const auto requirementName = utils::toLowerCase(context.parser.parseIdentifier(isIdentifier));
 
 	const auto match = requirementTypesToPDDL.right.find(requirementName);