diff --git a/src/raspberrypi/rascsi_interface.proto b/src/raspberrypi/rascsi_interface.proto
index ca6dc557..3ecfd1bb 100644
--- a/src/raspberrypi/rascsi_interface.proto
+++ b/src/raspberrypi/rascsi_interface.proto
@@ -178,8 +178,10 @@ message PbOperationParameter {
     map<string, string> description = 2;
     // There is no specific set of permitted values if empty
     repeated string permitted_values = 3;
-    // Optional default value. If there is no default the value is mandatory.
+    // Optional default value
     string default_value = 4;
+    // True if this parameter is mandatory
+    bool is_mandatory = 5;
 }
 
 // The list of parameters supported by an operation
diff --git a/src/raspberrypi/rascsi_response.cpp b/src/raspberrypi/rascsi_response.cpp
index 0404ba39..1d922220 100644
--- a/src/raspberrypi/rascsi_response.cpp
+++ b/src/raspberrypi/rascsi_response.cpp
@@ -378,7 +378,7 @@ PbOperationInfo *RascsiResponse::GetOperationInfo(PbResult& result)
 	CreateOperation(operation_info, meta_data, STOP, "Stop device, device-specific parameters are required");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "file", "Image file name");
+	AddOperationParameter(meta_data, "file", "Image file name", "", true);
 	CreateOperation(operation_info, meta_data, INSERT, "Insert medium, device-specific parameters are required");
 
 	meta_data = new PbOperationMetaData();
@@ -408,7 +408,7 @@ PbOperationInfo *RascsiResponse::GetOperationInfo(PbResult& result)
 	CreateOperation(operation_info, meta_data, DEFAULT_IMAGE_FILES_INFO, "Get information on available image files");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "file", "Image file name");
+	AddOperationParameter(meta_data, "file", "Image file name", "", true);
 	CreateOperation(operation_info, meta_data, IMAGE_FILE_INFO, "Get information on image file");
 
 	meta_data = new PbOperationMetaData();
@@ -424,59 +424,59 @@ PbOperationInfo *RascsiResponse::GetOperationInfo(PbResult& result)
 	CreateOperation(operation_info, meta_data, RESERVED_IDS_INFO, "Get list of reserved device IDs");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "folder", "Default image file folder name");
+	AddOperationParameter(meta_data, "folder", "Default image file folder name", "", true);
 	CreateOperation(operation_info, meta_data, DEFAULT_FOLDER, "Set default image file folder");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "level", "New log level");
+	AddOperationParameter(meta_data, "level", "New log level", "", true);
 	CreateOperation(operation_info, meta_data, LOG_LEVEL, "Set log level");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "ids", "Comma-separated device ID list");
+	AddOperationParameter(meta_data, "ids", "Comma-separated device ID list", "", true);
 	CreateOperation(operation_info, meta_data, RESERVE_IDS, "Reserve device IDs");
 
 	meta_data = new PbOperationMetaData();
-	PbOperationParameter *parameter = AddOperationParameter(meta_data, "mode", "Shutdown mode");
+	PbOperationParameter *parameter = AddOperationParameter(meta_data, "mode", "Shutdown mode", "", true);
 	parameter->add_permitted_values("rascsi");
 	parameter->add_permitted_values("system");
 	parameter->add_permitted_values("reboot");
 	CreateOperation(operation_info, meta_data, SHUT_DOWN, "Shut down or reboot");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "file", "Image file name");
-	AddOperationParameter(meta_data, "size", "Image file size in bytes");
+	AddOperationParameter(meta_data, "file", "Image file name", "", true);
+	AddOperationParameter(meta_data, "size", "Image file size in bytes", "", true);
 	parameter = AddOperationParameter(meta_data, "read_only",  "Read-only flag", "false");
 	parameter->add_permitted_values("true");
 	parameter->add_permitted_values("false");
 	CreateOperation(operation_info, meta_data, CREATE_IMAGE, "Create an image file");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "file", "Image file name");
+	AddOperationParameter(meta_data, "file", "Image file name", "", true);
 	CreateOperation(operation_info, meta_data, DELETE_IMAGE, "Delete image file");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "from", "Source image file name");
-	AddOperationParameter(meta_data, "to", "Destination image file name");
+	AddOperationParameter(meta_data, "from", "Source image file name", "", true);
+	AddOperationParameter(meta_data, "to", "Destination image file name", "", true);
 	CreateOperation(operation_info, meta_data, RENAME_IMAGE, "Rename image file");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "from", "Source image file name image file name");
-	AddOperationParameter(meta_data, "to", "Destination image file name");
+	AddOperationParameter(meta_data, "from", "Source image file name image file name", "", true);
+	AddOperationParameter(meta_data, "to", "Destination image file name", "", true);
 	parameter = AddOperationParameter(meta_data, "read_only", "Read-only flag", "false");
 	parameter->add_permitted_values("true");
 	parameter->add_permitted_values("false");
 	CreateOperation(operation_info, meta_data, COPY_IMAGE, "Copy image file");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "file", "Image file name");
+	AddOperationParameter(meta_data, "file", "Image file name", "", true);
 	CreateOperation(operation_info, meta_data, PROTECT_IMAGE, "Write-protect image file");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "file", "Image file name");
+	AddOperationParameter(meta_data, "file", "Image file name", "", true);
 	CreateOperation(operation_info, meta_data, UNPROTECT_IMAGE, "Make image file writable");
 
 	meta_data = new PbOperationMetaData();
-	AddOperationParameter(meta_data, "token", "Authentication token to be checked");
+	AddOperationParameter(meta_data, "token", "Authentication token to be checked", "", true);
 	CreateOperation(operation_info, meta_data, CHECK_AUTHENTICATION, "Check whether an authentication token is valid");
 
 	meta_data = new PbOperationMetaData();
@@ -500,7 +500,7 @@ void RascsiResponse::CreateOperation(PbOperationInfo *operation_info, PbOperatio
 }
 
 PbOperationParameter *RascsiResponse::AddOperationParameter(PbOperationMetaData *meta_data, const string& name,
-		const string& description, const string& default_value)
+		const string& description, const string& default_value, bool is_mandatory)
 {
 	PbOperationParameter *parameter = meta_data->add_parameters();
 	parameter->set_name(name);
@@ -508,6 +508,9 @@ PbOperationParameter *RascsiResponse::AddOperationParameter(PbOperationMetaData
 	if (!default_value.empty()) {
 		parameter->set_default_value(default_value);
 	}
+	else {
+		parameter->set_is_mandatory(is_mandatory);
+	}
 
 	return parameter;
 }
diff --git a/src/raspberrypi/rascsi_response.h b/src/raspberrypi/rascsi_response.h
index b9cea859..da607277 100644
--- a/src/raspberrypi/rascsi_response.h
+++ b/src/raspberrypi/rascsi_response.h
@@ -56,5 +56,5 @@ private:
 	void GetAvailableImages(PbResult& result, PbServerInfo&, const string&, int);
 	void CreateOperation(PbOperationInfo *, PbOperationMetaData *, const PbOperation&, const string&);
 	PbOperationParameter *AddOperationParameter(PbOperationMetaData *, const string&, const string&,
-			const string& = "");
+			const string& = "", bool = false);
 };
diff --git a/src/raspberrypi/rasctl_display.cpp b/src/raspberrypi/rasctl_display.cpp
index 21deb463..cf25e403 100644
--- a/src/raspberrypi/rasctl_display.cpp
+++ b/src/raspberrypi/rasctl_display.cpp
@@ -303,7 +303,7 @@ void RasctlDisplay::DisplayOperationInfo(const PbOperationInfo& operation_info)
 
 			for (const auto& parameter : operation.second.parameters()) {
 				cout << "    " << parameter.name() << ": "
-					<< (parameter.default_value().empty() ? "mandatory" : "optional");
+					<< (parameter.is_mandatory() ? "mandatory" : "optional");
 				if (!parameter.description().empty()) {
 					cout << " (" << parameter.description().at("en") << ")";
 				}