diff --git a/libsolidity/ast/ASTJsonConverter.cpp b/libsolidity/ast/ASTJsonConverter.cpp
index 6b459da4c..fc43976de 100644
--- a/libsolidity/ast/ASTJsonConverter.cpp
+++ b/libsolidity/ast/ASTJsonConverter.cpp
@@ -86,7 +86,7 @@ string ASTJsonConverter::sourceLocationToString(SourceLocation const& _location)
 
 ASTJsonConverter::ASTJsonConverter(
 	ASTNode const& _ast,
-	map<string, unsigned> const& _sourceIndices
+	map<string, unsigned> _sourceIndices
 ): m_ast(&_ast), m_sourceIndices(_sourceIndices)
 {
 	Json::Value children(Json::arrayValue);
diff --git a/libsolidity/ast/ASTJsonConverter.h b/libsolidity/ast/ASTJsonConverter.h
index 2e3046f14..ca4d9c2d6 100644
--- a/libsolidity/ast/ASTJsonConverter.h
+++ b/libsolidity/ast/ASTJsonConverter.h
@@ -45,7 +45,7 @@ public:
 	/// @a _sourceIndices is used to abbreviate source names in source locations.
 	explicit ASTJsonConverter(
 		ASTNode const& _ast,
-		std::map<std::string, unsigned> const& _sourceIndices = std::map<std::string, unsigned>()
+		std::map<std::string, unsigned> _sourceIndices = std::map<std::string, unsigned>()
 	);
 	/// Output the json representation of the AST to _stream.
 	void print(std::ostream& _stream);
@@ -141,7 +141,7 @@ private:
 	Json::Value m_astJson;
 	std::stack<Json::Value*> m_jsonNodePtrs;
 	ASTNode const* m_ast;
-	std::map<std::string, unsigned> const& m_sourceIndices;
+	std::map<std::string, unsigned> m_sourceIndices;
 };
 
 }