diff --git a/alib2cli/src/builtin/Dot.cpp b/alib2cli/src/builtin/Dot.cpp
index 20baf1d861a4140f6b93d0ca32696162284f739c..c274a3b2da646b424dd1e41549db70b413886889 100644
--- a/alib2cli/src/builtin/Dot.cpp
+++ b/alib2cli/src/builtin/Dot.cpp
@@ -65,15 +65,14 @@ void Dot::dot2 ( const std::string & data ) {
 	dot ( data, true );
 }
 
-void Dot::dot ( const std::string & data, const std::string& outputType, const std::string & outputFile ) {
-	std::string outputTypeLower;
-	std::transform ( outputType.begin ( ), outputType.end ( ), outputTypeLower.begin ( ), ::tolower );
+void Dot::dot ( const std::string & data, std::string outputType, const std::string & outputFile ) {
+	std::transform ( outputType.begin ( ), outputType.end ( ), outputType.begin ( ), ::tolower );
 
-	if ( std::find ( allowedOutputTypes.begin( ), allowedOutputTypes.end ( ), outputTypeLower ) == allowedOutputTypes.end ( ) ) {
-		throw exception::CommonException ( "Dot: Invalid output type." );
+	if ( std::find ( allowedOutputTypes.begin( ), allowedOutputTypes.end ( ), outputType ) == allowedOutputTypes.end ( ) ) {
+		throw exception::CommonException ( "Dot: Invalid output type (" + outputType + ")." );
 	}
 
-	run ( data, outputTypeLower, outputFile, false );
+	run ( data, outputType, outputFile, false );
 }
 
 
@@ -89,7 +88,7 @@ auto DotTx11 = registration::AbstractRegister < Dot, void, const std::string &,
 @param dot a string containing dot data\n\
 @param background a flag specifying whether to run in background (does not block CLI input)" );
 
-auto DotFile = registration::AbstractRegister < Dot, void, const std::string &, const std::string &, const std::string & > ( Dot::dot, abstraction::AlgorithmCategories::AlgorithmCategory::DEFAULT, "data", "outputType", "outputFile" ).setDocumentation (
+auto DotFile = registration::AbstractRegister < Dot, void, const std::string &, std::string, const std::string & > ( Dot::dot, abstraction::AlgorithmCategories::AlgorithmCategory::DEFAULT, "data", "outputType", "outputFile" ).setDocumentation (
 "Cli builtin command for DOT format visualization. Runs dot -T<outputType> -o <outputFile> and blocks the input until done.\n\
 \n\
 @param data a string containing dot data\n\
diff --git a/alib2cli/src/builtin/Dot.h b/alib2cli/src/builtin/Dot.h
index bb94741658724b9c90a230fe37e6a71311c71976..e9761f6ffa586a3a1b53a7d471ae91a47ac131b8 100644
--- a/alib2cli/src/builtin/Dot.h
+++ b/alib2cli/src/builtin/Dot.h
@@ -34,7 +34,7 @@ public:
 	 * \param outputType the type of dot created image
 	 * \param outputFile the destination file name
 	 */
-	static void dot ( const std::string & data, const std::string & outputType, const std::string & outputFile );
+	static void dot ( const std::string & data, std::string outputType, const std::string & outputFile );
 
 protected:
 	/** Allowed output types */