diff --git a/Machines/Utility/Typer.cpp b/Machines/Utility/Typer.cpp
index 1e290bef5..45efe35e7 100644
--- a/Machines/Utility/Typer.cpp
+++ b/Machines/Utility/Typer.cpp
@@ -59,7 +59,7 @@ void Typer::append(const std::string &string) {
 	// If the final character in the string is not Typer::EndString
 	// then this machine doesn't need Begin and End, so don't worry about it.
 	ssize_t insertion_position = ssize_t(string_.size());
-	if(string_.back() == Typer::EndString) --insertion_position;
+	if(!string_.empty() && string_.back() == Typer::EndString) --insertion_position;
 
 	string_.reserve(string_.size() + string.size());
 	for(const char c : string) {