diff --git a/src/sc_man.cpp b/src/sc_man.cpp
index 3860105dd..148f00637 100644
--- a/src/sc_man.cpp
+++ b/src/sc_man.cpp
@@ -239,7 +239,7 @@ void FScanner::PrepareScript ()
 	{
 		// If the last character in the buffer is a null character, change
 		// it to a newline. Otherwise, append a newline to the end.
-		if (ScriptBuffer[ScriptBuffer.Len() - 1] == '\0')
+		if (ScriptBuffer.Len() > 0 && ScriptBuffer[ScriptBuffer.Len() - 1] == '\0')
 		{
 			ScriptBuffer.LockBuffer()[ScriptBuffer.Len() - 1] = '\n';
 			ScriptBuffer.UnlockBuffer();