diff --git a/include/anthem/ASTUtils.h b/include/anthem/ASTUtils.h
index 550415d..d9d0af6 100644
--- a/include/anthem/ASTUtils.h
+++ b/include/anthem/ASTUtils.h
@@ -26,7 +26,7 @@ class VariableStack
 		void push(Layer layer);
 		void pop();
 
-		std::experimental::optional<ast::VariableDeclaration *> findVariableDeclaration(const char *variableName) const;
+		std::experimental::optional<ast::VariableDeclaration *> findUserVariableDeclaration(const char *variableName) const;
 		bool contains(const ast::VariableDeclaration &variableDeclaration) const;
 
 	private:
diff --git a/include/anthem/Term.h b/include/anthem/Term.h
index c220cf3..f92e245 100644
--- a/include/anthem/Term.h
+++ b/include/anthem/Term.h
@@ -85,7 +85,7 @@ struct TermTranslateVisitor
 
 	std::experimental::optional<ast::Term> visit(const Clingo::AST::Variable &variable, const Clingo::AST::Term &, Context &, RuleContext &ruleContext, const ast::VariableStack &variableStack)
 	{
-		const auto matchingVariableDeclaration = variableStack.findVariableDeclaration(variable.name);
+		const auto matchingVariableDeclaration = variableStack.findUserVariableDeclaration(variable.name);
 		const auto isAnonymousVariable = (strcmp(variable.name, "_") == 0);
 		const auto isUndeclaredUserVariable = !matchingVariableDeclaration;
 		const auto isUndeclared = isAnonymousVariable || isUndeclaredUserVariable;
diff --git a/src/anthem/ASTUtils.cpp b/src/anthem/ASTUtils.cpp
index f7b84a3..61cb799 100644
--- a/src/anthem/ASTUtils.cpp
+++ b/src/anthem/ASTUtils.cpp
@@ -27,12 +27,13 @@ void VariableStack::pop()
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-std::experimental::optional<ast::VariableDeclaration *> VariableStack::findVariableDeclaration(const char *variableName) const
+std::experimental::optional<ast::VariableDeclaration *> VariableStack::findUserVariableDeclaration(const char *variableName) const
 {
 	const auto variableNameMatches =
 		[&variableName](const auto &variableDeclaration)
 		{
-			return variableDeclaration->name == variableName;
+			return variableDeclaration->type == VariableDeclaration::Type::UserDefined
+				&& variableDeclaration->name == variableName;
 		};
 
 	for (auto i = m_layers.rbegin(); i != m_layers.rend(); i++)