diff --git a/src/lcf/log_handler.h b/src/lcf/log_handler.h
index c6eb69ac..26a2165d 100644
--- a/src/lcf/log_handler.h
+++ b/src/lcf/log_handler.h
@@ -11,6 +11,7 @@
 #define LCF_OUTPUT_H
 
 #include "string_view.h"
+#include "enum_tags.h"
 
 namespace lcf {
 namespace LogHandler {
@@ -22,15 +23,24 @@ enum class Level {
 	Highest
 };
 
-using LogHandlerFn = void (*)(Level level, StringView message);
+static constexpr auto kLevelTags = lcf::makeEnumTags<Level>(
+	"Debug",
+	"Warning",
+	"Error",
+	"Highest"
+);
+
+using UserData = void*;
+using LogHandlerFn = void (*)(Level level, StringView message, UserData userdata);
 
 /**
  * Sets the output handler for all lcf logging.
  * The default handler prints to standard error.
  *
  * @param fn New output handler. nullptr for default handler.
+ * @param userdata Passed to the log handler function. Is not touched by liblcf.
  */
-void SetHandler(LogHandlerFn fn);
+void SetHandler(LogHandlerFn fn, UserData userdata = nullptr);
 
 /**
  * Only report issues that have at least this log level.
diff --git a/src/log_handler.cpp b/src/log_handler.cpp
index 33272c8c..623aad8d 100644
--- a/src/log_handler.cpp
+++ b/src/log_handler.cpp
@@ -16,7 +16,7 @@
 namespace lcf {
 namespace LogHandler {
 namespace {
-	void DefaultHandler(lcf::LogHandler::Level level, StringView message) {
+	void DefaultHandler(LogHandler::Level level, StringView message, UserData) {
 		switch (level) {
 			case Level::Debug:
 				std::cerr << "Debug: ";
@@ -35,13 +35,16 @@ namespace {
 
 	Level level = Level::Debug;
 	LogHandlerFn output_fn = DefaultHandler;
+	UserData output_userdata = nullptr;
 }
 
-void SetHandler(LogHandlerFn fn) {
+void SetHandler(LogHandlerFn fn, UserData userdata) {
 	if (!fn) {
 		output_fn = DefaultHandler;
+		output_userdata = nullptr;
 	} else {
 		output_fn = fn;
+		output_userdata = userdata;
 	}
 }
 
@@ -60,7 +63,7 @@ namespace {
 			return {};
 		}
 
-		return std::string(buf, static_cast<unsigned int>(result) < sizeof(buf) ? result : sizeof(buf));
+		return {buf, static_cast<unsigned int>(result) < sizeof(buf) ? result : sizeof(buf)};
 	}
 }
 
@@ -69,7 +72,7 @@ void Debug(const char* fmt, ...) {
 		va_list args;
 		va_start(args, fmt);
 		auto msg = format_string(fmt, args);
-		LogHandler::output_fn(LogHandler::Level::Debug, msg);
+		LogHandler::output_fn(LogHandler::Level::Debug, msg, LogHandler::output_userdata);
 		va_end(args);
 	}
 }
@@ -79,7 +82,7 @@ void Warning(const char* fmt, ...) {
 		va_list args;
 		va_start(args, fmt);
 		auto msg = format_string(fmt, args);
-		LogHandler::output_fn(LogHandler::Level::Warning, msg);
+		LogHandler::output_fn(LogHandler::Level::Warning, msg, LogHandler::output_userdata);
 		va_end(args);
 	}
 }
@@ -89,7 +92,7 @@ void Error(const char* fmt, ...) {
 		va_list args;
 		va_start(args, fmt);
 		auto msg = format_string(fmt, args);
-		LogHandler::output_fn(LogHandler::Level::Error, msg);
+		LogHandler::output_fn(LogHandler::Level::Error, msg, LogHandler::output_userdata);
 		va_end(args);
 	}
 }