diff --git a/Makefile b/Makefile
index 829c7a9..bfad6f9 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@ MAKEFLAGS="-j $(grep -c ^processor /proc/cpuinfo)"
 CXXFLAGS:=$(CXXFLAGS) -std=c++20 -Wall -Wextra -Werror=switch -Werror=return-type -Werror=unused-result
 CPPFLAGS:=$(CPPFLAGS) -Ilib/expected/ -Ilib/ut/ -Ilib/midi/include -Isrc/
 RELEASE_FLAGS=-O3
-DEBUG_FLAGS=-O0 -ggdb
+DEBUG_FLAGS=-O0 -ggdb -fsanitize=undefined
 CXX=g++
 
 LDFLAGS=-L./lib/midi/
diff --git a/etc/tools/test.py b/etc/tools/test.py
index 5c35402..82934f2 100755
--- a/etc/tools/test.py
+++ b/etc/tools/test.py
@@ -151,6 +151,10 @@ def main():
         print("[ERROR] Expected test case")
         exit(1)
 
+    interpreter = os.getenv("INTERPRETER")
+    if interpreter:
+        Interpreter = interpreter
+
     for path in argv[2:]:
         if os.path.exists(path):
             if os.path.isdir(path):
diff --git a/src/musique.hh b/src/musique.hh
index 031d42a..9ebc20c 100644
--- a/src/musique.hh
+++ b/src/musique.hh
@@ -561,6 +561,9 @@ struct Parser
 	/// Parse infix expression
 	Result<Ast> parse_infix_expression();
 
+	/// Parse either index expression or atomic expression
+	Result<Ast> parse_index_expression();
+
 	/// Parse function call, literal etc
 	Result<Ast> parse_atomic_expression();
 
diff --git a/src/parser.cc b/src/parser.cc
index e45fd87..a21611d 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -119,10 +119,11 @@ Result<Ast> Parser::parse_variable_declaration()
 
 Result<Ast> Parser::parse_infix_expression()
 {
-	auto atomics = Try(parse_many(*this, &Parser::parse_atomic_expression, std::nullopt, At_Least::One));
+	auto atomics = Try(parse_many(*this, &Parser::parse_index_expression, std::nullopt, At_Least::One));
 	auto lhs = wrap_if_several(std::move(atomics), Ast::call);
 
 	if (expect(Token::Type::Operator) || expect(Token::Type::Keyword, "and") || expect(Token::Type::Keyword, "or")) {
+		assert(not expect(Token::Type::Operator, "."), "This should be handled by parse_index_expression");
 		auto op = consume();
 		return parse_expression().map([&](Ast rhs) {
 			return Ast::binary(std::move(op), std::move(lhs), std::move(rhs));
@@ -132,6 +133,23 @@ Result<Ast> Parser::parse_infix_expression()
 	return lhs;
 }
 
+Result<Ast> Parser::parse_index_expression()
+{
+	auto result = Try(parse_atomic_expression());
+
+	while (expect(Token::Type::Operator, ".")) {
+		auto op = consume();
+		if (auto maybe_index = parse_atomic_expression(); maybe_index.has_value()) {
+			result = Ast::binary(std::move(op), std::move(result), *std::move(maybe_index));
+		} else {
+			// TODO Report that error occured during parsing of index expression
+			return std::move(maybe_index).error();
+		}
+	}
+
+	return result;
+}
+
 Result<Ast> Parser::parse_atomic_expression()
 {
 	switch (Try(peek_type())) {