diff --git a/README.md b/README.md
index b139a91..4a2fe07 100644
--- a/README.md
+++ b/README.md
@@ -53,7 +53,7 @@ The `[options]` are listed below:
 
 | **option**                        | **explanation**                                                                                                                   |
 |-----------------------------------|-----------------------------------------------------------------------------------------------------------------------------------|
-| `-l` [ `--language` ]             | Specify the input language (`SAS` or `PDDL`). Omit for automatic detection.                                                       |
+| `-l` [ `--language` ]             | Specify the input language (`sas` or `pddl`). Omit for automatic detection.                                                       |
 | `--warning-level` arg (=`normal`) | Specify whether to output warnings normally (`normal`), to treat them as critical errors (`error`), or to ignore them (`ignore`). |
 | `--color` arg (=`auto`)           | Specify whether to colorize the output (`always`, `never`, or `auto`).                                                            |
 
diff --git a/apps/plasp-app/main.cpp b/apps/plasp-app/main.cpp
index 384da37..7bacfae 100644
--- a/apps/plasp-app/main.cpp
+++ b/apps/plasp-app/main.cpp
@@ -21,7 +21,7 @@ int main(int argc, char **argv)
 		("help,h", "Display this help message.")
 		("version,v", "Display version information.")
 		("input,i", po::value<std::vector<std::string>>(), "Specify the PDDL or SAS input file.")
-		("language,l", po::value<std::string>(), "Specify the input language (SAS or PDDL). Omit for automatic detection.")
+		("language,l", po::value<std::string>(), "Specify the input language (sas or pddl). Omit for automatic detection.")
 		("warning-level", po::value<std::string>()->default_value("normal"), "Specify whether to output warnings normally (normal), to treat them as critical errors (error), or to ignore them (ignore).")
 		("color", po::value<std::string>()->default_value("auto"), "Specify whether to colorize the output (always, never, or auto).");
 
diff --git a/src/plasp/Language.cpp b/src/plasp/Language.cpp
index c23924e..6caaeb0 100644
--- a/src/plasp/Language.cpp
+++ b/src/plasp/Language.cpp
@@ -17,9 +17,9 @@ using LanguageNames = boost::bimap<Language::Type, std::string>;
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 const LanguageNames languageNames = boost::assign::list_of<LanguageNames::relation>
-	(Language::Type::PDDL, "PDDL")
-	(Language::Type::SAS, "SAS")
-	(Language::Type::Unknown, "Unknown");
+	(Language::Type::PDDL, "pddl")
+	(Language::Type::SAS, "sas")
+	(Language::Type::Unknown, "unknown");
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
@@ -28,7 +28,7 @@ std::string Language::toString(Language::Type language)
 	const auto match = languageNames.left.find(language);
 
 	if (match == languageNames.left.end())
-		return "Unknown";
+		return "unknown";
 
 	return match->second;
 }