diff --git a/CompilerStack.cpp b/CompilerStack.cpp
index 41ae56036..d46754856 100644
--- a/CompilerStack.cpp
+++ b/CompilerStack.cpp
@@ -82,7 +82,7 @@ void CompilerStack::parse(string const& _sourceCode)
 	parse();
 }
 
-vector<string> CompilerStack::getContractNames()
+vector<string> CompilerStack::getContractNames() const
 {
 	if (!m_parseSuccessful)
 		BOOST_THROW_EXCEPTION(CompilerError() << errinfo_comment("Parsing was not successful."));
@@ -116,29 +116,29 @@ bytes const& CompilerStack::compile(string const& _sourceCode, bool _optimize)
 	return getBytecode();
 }
 
-bytes const& CompilerStack::getBytecode(string const& _contractName)
+bytes const& CompilerStack::getBytecode(string const& _contractName) const
 {
 	return getContract(_contractName).bytecode;
 }
 
-void CompilerStack::streamAssembly(ostream& _outStream, string const& _contractName)
+void CompilerStack::streamAssembly(ostream& _outStream, string const& _contractName) const
 {
 	getContract(_contractName).compiler->streamAssembly(_outStream);
 }
 
-string const& CompilerStack::getInterface(std::string const& _contractName)
+string const& CompilerStack::getInterface(string const& _contractName) const
 {
 	return getJsonDocumentation(_contractName, DocumentationType::ABI_INTERFACE);
 }
 
-std::string const& CompilerStack::getJsonDocumentation(std::string const& _contractName, DocumentationType _type)
+string const& CompilerStack::getJsonDocumentation(string const& _contractName, DocumentationType _type) const
 {
 	if (!m_parseSuccessful)
 		BOOST_THROW_EXCEPTION(CompilerError() << errinfo_comment("Parsing was not successful."));
 
-	Contract& contract = getContract(_contractName);
+	Contract const& contract = getContract(_contractName);
 
-	std::unique_ptr<string>* doc;
+	std::unique_ptr<string const>* doc;
 	switch (_type)
 	{
 	case DocumentationType::NATSPEC_USER:
@@ -158,12 +158,12 @@ std::string const& CompilerStack::getJsonDocumentation(std::string const& _contr
 	return *(*doc);
 }
 
-Scanner const& CompilerStack::getScanner(string const& _sourceName)
+Scanner const& CompilerStack::getScanner(string const& _sourceName) const
 {
 	return *getSource(_sourceName).scanner;
 }
 
-SourceUnit& CompilerStack::getAST(string const& _sourceName)
+SourceUnit const& CompilerStack::getAST(string const& _sourceName) const
 {
 	return *getSource(_sourceName).ast;
 }
@@ -217,7 +217,7 @@ void CompilerStack::resolveImports()
 	swap(m_sourceOrder, sourceOrder);
 }
 
-CompilerStack::Contract& CompilerStack::getContract(string const& _contractName)
+CompilerStack::Contract const& CompilerStack::getContract(string const& _contractName) const
 {
 	if (m_contracts.empty())
 		BOOST_THROW_EXCEPTION(CompilerError() << errinfo_comment("No compiled contracts found."));
@@ -229,7 +229,7 @@ CompilerStack::Contract& CompilerStack::getContract(string const& _contractName)
 	return it->second;
 }
 
-CompilerStack::Source& CompilerStack::getSource(string const& _sourceName)
+CompilerStack::Source const& CompilerStack::getSource(string const& _sourceName) const
 {
 	auto it = m_sources.find(_sourceName);
 	if (it == m_sources.end())
diff --git a/CompilerStack.h b/CompilerStack.h
index 82d275498..b6c34f1ac 100644
--- a/CompilerStack.h
+++ b/CompilerStack.h
@@ -64,7 +64,7 @@ public:
 	/// Sets the given source code as the only source unit and parses it.
 	void parse(std::string const& _sourceCode);
 	/// Returns a list of the contract names in the sources.
-	std::vector<std::string> getContractNames();
+	std::vector<std::string> getContractNames() const;
 
 	/// Compiles the source units that were previously added and parsed.
 	void compile(bool _optimize = false);
@@ -72,23 +72,23 @@ public:
 	/// @returns the compiled bytecode
 	bytes const& compile(std::string const& _sourceCode, bool _optimize = false);
 
-	bytes const& getBytecode(std::string const& _contractName = "");
+	bytes const& getBytecode(std::string const& _contractName = "") const;
 	/// Streams a verbose version of the assembly to @a _outStream.
 	/// Prerequisite: Successful compilation.
-	void streamAssembly(std::ostream& _outStream, std::string const& _contractName = "");
+	void streamAssembly(std::ostream& _outStream, std::string const& _contractName = "") const;
 
 	/// Returns a string representing the contract interface in JSON.
 	/// Prerequisite: Successful call to parse or compile.
-	std::string const& getInterface(std::string const& _contractName = "");
+	std::string const& getInterface(std::string const& _contractName = "") const;
 	/// Returns a string representing the contract's documentation in JSON.
 	/// Prerequisite: Successful call to parse or compile.
 	/// @param type The type of the documentation to get.
 	/// Can be one of 3 types defined at @c DocumentationType
-	std::string const& getJsonDocumentation(std::string const& _contractName, DocumentationType _type);
+	std::string const& getJsonDocumentation(std::string const& _contractName, DocumentationType _type) const;
 
 	/// Returns the previously used scanner, useful for counting lines during error reporting.
-	Scanner const& getScanner(std::string const& _sourceName = "");
-	SourceUnit& getAST(std::string const& _sourceName = "");
+	Scanner const& getScanner(std::string const& _sourceName = "") const;
+	SourceUnit const& getAST(std::string const& _sourceName = "") const;
 
 	/// Compile the given @a _sourceCode to bytecode. If a scanner is provided, it is used for
 	/// scanning the source code - this is useful for printing exception information.
@@ -112,9 +112,9 @@ private:
 		std::shared_ptr<Compiler> compiler;
 		bytes bytecode;
 		std::shared_ptr<InterfaceHandler> interfaceHandler;
-		std::unique_ptr<std::string> interface;
-		std::unique_ptr<std::string> userDocumentation;
-		std::unique_ptr<std::string> devDocumentation;
+		mutable std::unique_ptr<std::string const> interface;
+		mutable std::unique_ptr<std::string const> userDocumentation;
+		mutable std::unique_ptr<std::string const> devDocumentation;
 
 		Contract();
 	};
@@ -122,14 +122,14 @@ private:
 	void reset(bool _keepSources = false);
 	void resolveImports();
 
-	Contract& getContract(std::string const& _contractName = "");
-	Source& getSource(std::string const& _sourceName = "");
+	Contract const& getContract(std::string const& _contractName = "") const;
+	Source const& getSource(std::string const& _sourceName = "") const;
 
 	bool m_parseSuccessful;
-	std::map<std::string, Source> m_sources;
+	std::map<std::string const, Source> m_sources;
 	std::shared_ptr<GlobalContext> m_globalContext;
 	std::vector<Source const*> m_sourceOrder;
-	std::map<std::string, Contract> m_contracts;
+	std::map<std::string const, Contract> m_contracts;
 };
 
 }
diff --git a/Types.h b/Types.h
index 42ead008a..f4ad804d1 100644
--- a/Types.h
+++ b/Types.h
@@ -279,7 +279,7 @@ public:
 	virtual bool canLiveOutsideStorage() const override { return false; }
 	virtual unsigned getSizeOnStack() const override;
 
-	Location getLocation() const { return m_location; }
+	Location const& getLocation() const { return m_location; }
 
 private:
 	TypePointers m_parameterTypes;