diff --git a/builtin/settingtypes.txt b/builtin/settingtypes.txt
index 4254603e2..eefd3490c 100644
--- a/builtin/settingtypes.txt
+++ b/builtin/settingtypes.txt
@@ -1319,6 +1319,12 @@ language (Language) enum   ,be,ca,cs,da,de,dv,en,eo,es,et,fr,he,hu,id,it,ja,jbo,
 #    -    verbose
 debug_log_level (Debug log level) enum action ,none,error,warning,action,info,verbose
 
+#    If the file size of debug.txt exceeds the number of megabytes specified in
+#    this setting when it is opened, the file is moved to debug.txt.1,
+#    deleting an older debug.txt.1 if it exists.
+#    debug.txt is only moved if this setting is positive.
+debug_log_size_max (Debug log file size threshold) int 50
+
 #    IPv6 support.
 enable_ipv6 (IPv6) bool true
 
diff --git a/src/defaultsettings.cpp b/src/defaultsettings.cpp
index 7756bc45d..0c51610c9 100644
--- a/src/defaultsettings.cpp
+++ b/src/defaultsettings.cpp
@@ -385,6 +385,7 @@ void set_default_settings(Settings *settings)
 	settings->setDefault("ignore_world_load_errors", "false");
 	settings->setDefault("remote_media", "");
 	settings->setDefault("debug_log_level", "action");
+	settings->setDefault("debug_log_size_max", "50");
 	settings->setDefault("emergequeue_limit_total", "512");
 	settings->setDefault("emergequeue_limit_diskonly", "64");
 	settings->setDefault("emergequeue_limit_generate", "64");
diff --git a/src/log.cpp b/src/log.cpp
index c84a847a5..30344b4df 100644
--- a/src/log.cpp
+++ b/src/log.cpp
@@ -310,16 +310,32 @@ void Logger::logToOutputs(LogLevel lev, const std::string &combined,
 //// *LogOutput methods
 ////
 
-void FileLogOutput::open(const std::string &filename)
+void FileLogOutput::setFile(const std::string &filename, s64 file_size_max)
 {
-	m_stream.open(filename.c_str(), std::ios::app | std::ios::ate);
+	// Only move debug.txt if there is a valid maximum file size
+	bool is_too_large = false;
+	if (file_size_max > 0) {
+		std::ifstream ifile(filename, std::ios::binary | std::ios::ate);
+		is_too_large = ifile.tellg() > file_size_max;
+		ifile.close();
+	}
+
+	if (is_too_large) {
+		std::string filename_secondary = filename + ".1";
+		actionstream << "The log file grew too big; it is moved to " <<
+			filename_secondary << std::endl;
+		remove(filename_secondary.c_str());
+		rename(filename.c_str(), filename_secondary.c_str());
+	}
+	m_stream.open(filename, std::ios::app | std::ios::ate);
+
 	if (!m_stream.good())
 		throw FileNotGoodException("Failed to open log file " +
 			filename + ": " + strerror(errno));
 	m_stream << "\n\n"
-		   "-------------" << std::endl
-		<< "  Separator" << std::endl
-		<< "-------------\n" << std::endl;
+		"-------------" << std::endl <<
+		"  Separator" << std::endl <<
+		"-------------\n" << std::endl;
 }
 
 
diff --git a/src/log.h b/src/log.h
index 1427d1364..6350d8a86 100644
--- a/src/log.h
+++ b/src/log.h
@@ -165,7 +165,7 @@ private:
 
 class FileLogOutput : public ICombinedLogOutput {
 public:
-	void open(const std::string &filename);
+	void setFile(const std::string &filename, s64 file_size_max);
 
 	void logRaw(LogLevel lev, const std::string &line)
 	{
diff --git a/src/main.cpp b/src/main.cpp
index bd83f9638..6323fa50e 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -172,7 +172,7 @@ int main(int argc, char *argv[])
 		} else {
 			errorstream << "Invalid --worldlist value: "
 				<< cmd_args.get("worldlist") << std::endl;
-			return 1; 
+			return 1;
 		}
 		return 0;
 	}
@@ -426,7 +426,7 @@ static bool setup_log_params(const Settings &cmd_args)
 		} else {
 			errorstream << "Invalid color mode: " << color_mode << std::endl;
 			return false;
-		}			
+		}
 	}
 
 	// If trace is enabled, enable logging of certain things
@@ -580,9 +580,8 @@ static void init_log_streams(const Settings &cmd_args)
 			"using maximum." << std::endl;
 	}
 
-	verbosestream << "log_filename = " << log_filename << std::endl;
-
-	file_log_output.open(log_filename);
+	file_log_output.setFile(log_filename,
+		g_settings->getU64("debug_log_size_max") * 1000000);
 	g_logger.addOutputMaxLevel(&file_log_output, log_level);
 }