diff --git a/libsolidity/interface/FileReader.cpp b/libsolidity/interface/FileReader.cpp
index 264d2507e..295d02da4 100644
--- a/libsolidity/interface/FileReader.cpp
+++ b/libsolidity/interface/FileReader.cpp
@@ -42,7 +42,7 @@ void FileReader::setSources(StringMap _sources)
 	m_sourceCodes = std::move(_sources);
 }
 
-ReadCallback::Result FileReader::readFile(string const& _kind, string const& _path)
+ReadCallback::Result FileReader::readFile(string const& _kind, string const& _sourceUnitName)
 {
 	try
 	{
@@ -51,11 +51,11 @@ ReadCallback::Result FileReader::readFile(string const& _kind, string const& _pa
 				"ReadFile callback used as callback kind " +
 				_kind
 			));
-		string validPath = _path;
-		if (validPath.find("file://") == 0)
-			validPath.erase(0, 7);
+		string strippedSourceUnitName = _sourceUnitName;
+		if (strippedSourceUnitName.find("file://") == 0)
+			strippedSourceUnitName.erase(0, 7);
 
-		auto canonicalPath = boost::filesystem::weakly_canonical(m_basePath / validPath);
+		auto canonicalPath = boost::filesystem::weakly_canonical(m_basePath / strippedSourceUnitName);
 		bool isAllowed = false;
 		for (auto const& allowedDir: m_allowedDirectories)
 		{
@@ -80,7 +80,7 @@ ReadCallback::Result FileReader::readFile(string const& _kind, string const& _pa
 
 		// NOTE: we ignore the FileNotFound exception as we manually check above
 		auto contents = readFileAsString(canonicalPath.string());
-		m_sourceCodes[_path] = contents;
+		m_sourceCodes[_sourceUnitName] = contents;
 		return ReadCallback::Result{true, contents};
 	}
 	catch (util::Exception const& _exception)
diff --git a/libsolidity/interface/FileReader.h b/libsolidity/interface/FileReader.h
index c5ea4d71d..5aca710db 100644
--- a/libsolidity/interface/FileReader.h
+++ b/libsolidity/interface/FileReader.h
@@ -62,14 +62,21 @@ public:
 	SourceCode const& sourceCode(SourceUnitName const& _sourceUnitName) const { return m_sourceCodes.at(_sourceUnitName); }
 
 	/// Resets all sources to the given map of source unit ID to source codes.
+	/// Does not enforce @a allowedDirectories().
 	void setSources(StringMap _sources);
 
 	/// Adds the source code for a given source unit ID.
+	/// Does not enforce @a allowedDirectories().
 	void setSource(boost::filesystem::path const& _path, SourceCode _source);
 
-	/// Reads a given file at @p _path of kind @p _kind from the local filesystem and returns the result.
-	/// @p _kind must always be passed as "source".
-	frontend::ReadCallback::Result readFile(std::string const& _kind, std::string const& _path);
+	/// Receives a @p _sourceUnitName that refers to a source unit in compiler's virtual filesystem
+	/// and attempts to interpret it as a path and read the corresponding file from disk.
+	/// The read will only succeed if the canonical path of the file is within one of the @a allowedDirectories().
+	/// @param _kind must be equal to "source". Other values are not supported.
+	/// @return Content of the loaded file or an error message. If the operation succeeds, a copy of
+	/// the content is retained in @a sourceCodes() under the key of @a _sourceUnitName. If the key
+	/// already exists, previous content is discarded.
+	frontend::ReadCallback::Result readFile(std::string const& _kind, std::string const& _sourceUnitName);
 
 	frontend::ReadCallback::Callback reader()
 	{