diff --git a/src/raspberrypi/rascsi_interface.proto b/src/raspberrypi/rascsi_interface.proto
index 010b1a29..6aa23a82 100644
--- a/src/raspberrypi/rascsi_interface.proto
+++ b/src/raspberrypi/rascsi_interface.proto
@@ -61,8 +61,7 @@ enum PbOperation {
     RESERVE = 14;
     // Create an image file. The image file must not yet exist.
     // PbCommand.params(0) contains the filename, PbCommand.params(1) contains the file size in bytes.
-    // PbCommand.params(2) is optional (default is false) and controls the file permissions.
-    // If "true" (case-insensitive) a read-only file is created.
+    // PbCommand.params(2) controls the file permissions. If "true" (case-insensitive) a read-only file is created.
     // The filename is relative to the default image folder and must not contain a slash.
     // The file size must be a multiple of 512.
     CREATE_IMAGE = 15;
diff --git a/src/raspberrypi/rasctl.cpp b/src/raspberrypi/rasctl.cpp
index 15c0d289..9f1dd58a 100644
--- a/src/raspberrypi/rasctl.cpp
+++ b/src/raspberrypi/rasctl.cpp
@@ -216,6 +216,12 @@ void CommandCreateImage(const string&hostname, int port, const string& image_par
 		command.add_params(image_params.substr(0, separatorPos));
 		command.add_params(image_params.substr(separatorPos + 1));
 	}
+	else {
+		cerr << "Error: Invalid file description '" << image_params << "', format is NAME:SIZE" << endl;
+		exit(EXIT_FAILURE);
+	}
+
+	command.add_params("false");
 
     PbResult result;
     SendCommand(hostname.c_str(), port, command, result);
@@ -242,6 +248,10 @@ void CommandRenameImage(const string&hostname, int port, const string& image_par
 		command.add_params(image_params.substr(0, separatorPos));
 		command.add_params(image_params.substr(separatorPos + 1));
 	}
+	else {
+		cerr << "Error: Invalid file description '" << image_params << "', format is OLD_NAME:NEW_NAME" << endl;
+		exit(EXIT_FAILURE);
+	}
 
     PbResult result;
     SendCommand(hostname.c_str(), port, command, result);