diff --git a/include/plasp/pddl/expressions/PrimitiveType.h b/include/plasp/pddl/expressions/PrimitiveType.h
index 8fb7c4a..45a1706 100644
--- a/include/plasp/pddl/expressions/PrimitiveType.h
+++ b/include/plasp/pddl/expressions/PrimitiveType.h
@@ -25,7 +25,7 @@ class PrimitiveType: public Expression
 		static void parseDeclaration(Context &context, Domain &domain);
 		static void parseTypedDeclaration(Context &context, Domain &domain);
 
-		static PrimitiveType *parseAndFindOrCreate(Context &context, Domain &domain);
+		static PrimitiveType *parseAndFind(Context &context, Domain &domain);
 
 	public:
 		PrimitiveType();
diff --git a/src/plasp/pddl/expressions/Constant.cpp b/src/plasp/pddl/expressions/Constant.cpp
index ac23a2a..be26c6b 100644
--- a/src/plasp/pddl/expressions/Constant.cpp
+++ b/src/plasp/pddl/expressions/Constant.cpp
@@ -84,7 +84,7 @@ void Constant::parseTypedDeclaration(Context &context, Domain &domain, Constants
 		return;
 
 	// If existing, parse and store parent type
-	auto *type = PrimitiveType::parseAndFindOrCreate(context, domain);
+	auto *type = PrimitiveType::parseAndFind(context, domain);
 
 	// Assign parent type to all types that were previously flagged
 	std::for_each(constants.begin(), constants.end(),
diff --git a/src/plasp/pddl/expressions/PrimitiveType.cpp b/src/plasp/pddl/expressions/PrimitiveType.cpp
index 11a7bd7..86c8141 100644
--- a/src/plasp/pddl/expressions/PrimitiveType.cpp
+++ b/src/plasp/pddl/expressions/PrimitiveType.cpp
@@ -85,7 +85,7 @@ void PrimitiveType::parseTypedDeclaration(Context &context, Domain &domain)
 		throw utils::ParserException(context.parser, "Typing used but not declared as a requirement");
 
 	// If existing, parse and store parent type
-	auto *parentType = parseAndFindOrCreate(context, domain);
+	auto *parentType = parseAndFind(context, domain);
 
 	parentType->setDirty(false);
 
@@ -103,7 +103,7 @@ void PrimitiveType::parseTypedDeclaration(Context &context, Domain &domain)
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-PrimitiveType *PrimitiveType::parseAndFindOrCreate(Context &context, Domain &domain)
+PrimitiveType *PrimitiveType::parseAndFind(Context &context, Domain &domain)
 {
 	auto &types = domain.types();
 
@@ -122,8 +122,11 @@ PrimitiveType *PrimitiveType::parseAndFindOrCreate(Context &context, Domain &dom
 
 	if (match == types.cend())
 	{
-		// If necessary, insert new primitive type but don't declare it
-		types.emplace_back(std::make_unique<expressions::PrimitiveType>(typeName));
+		// Only "object" is allowed as an implicit type
+		if (typeName == "object")
+			types.emplace_back(std::make_unique<expressions::PrimitiveType>(typeName));
+		else
+			throw utils::ParserException(context.parser, "Type \"" + typeName + "\" used but never declared");
 
 		return types.back().get();
 	}
diff --git a/src/plasp/pddl/expressions/Type.cpp b/src/plasp/pddl/expressions/Type.cpp
index b65c6ca..18ededa 100644
--- a/src/plasp/pddl/expressions/Type.cpp
+++ b/src/plasp/pddl/expressions/Type.cpp
@@ -20,7 +20,7 @@ namespace expressions
 
 ExpressionPointer parseExistingPrimitiveType(Context &context, ExpressionContext &expressionContext)
 {
-	auto *primitiveType = PrimitiveType::parseAndFindOrCreate(context, expressionContext.domain);
+	auto *primitiveType = PrimitiveType::parseAndFind(context, expressionContext.domain);
 
 	return std::make_unique<Reference<PrimitiveType>>(primitiveType);
 }
diff --git a/src/plasp/pddl/expressions/Variable.cpp b/src/plasp/pddl/expressions/Variable.cpp
index e5da42e..4a6b0f6 100644
--- a/src/plasp/pddl/expressions/Variable.cpp
+++ b/src/plasp/pddl/expressions/Variable.cpp
@@ -100,7 +100,7 @@ void Variable::parseTypedDeclaration(Context &context, ExpressionContext &expres
 	}
 
 	// Parse primitive type
-	const auto *type = PrimitiveType::parseAndFindOrCreate(context, expressionContext.domain);
+	const auto *type = PrimitiveType::parseAndFind(context, expressionContext.domain);
 
 	setType(type);
 }