diff --git a/aegisub/libaegisub/common/charset.cpp b/aegisub/libaegisub/common/charset.cpp
index 3e1e961f0..83c80b97a 100644
--- a/aegisub/libaegisub/common/charset.cpp
+++ b/aegisub/libaegisub/common/charset.cpp
@@ -28,7 +28,7 @@ std::string Detect(const std::string &file) {
 	return ucd.Single();
 }
 
-void DetectAll(const std::string file, CharsetListDetected &list) {
+void DetectAll(const std::string& file, CharsetListDetected &list) {
 	UCDetect ucd(file);
 	ucd.List(list);
 }
diff --git a/aegisub/libaegisub/common/log.cpp b/aegisub/libaegisub/common/log.cpp
index 88a94eb03..ac3002791 100644
--- a/aegisub/libaegisub/common/log.cpp
+++ b/aegisub/libaegisub/common/log.cpp
@@ -63,7 +63,7 @@ SinkMessage::~SinkMessage() {
 }
 
 
-LogSink::LogSink(const std::string dir_log): dir_log(dir_log) {
+LogSink::LogSink(const std::string& dir_log): dir_log(dir_log) {
 	util::time_log(time_start);
 }
 
diff --git a/aegisub/libaegisub/include/libaegisub/charset.h b/aegisub/libaegisub/include/libaegisub/charset.h
index 83fe98507..e41cd8da4 100644
--- a/aegisub/libaegisub/include/libaegisub/charset.h
+++ b/aegisub/libaegisub/include/libaegisub/charset.h
@@ -36,10 +36,10 @@ DEFINE_SIMPLE_EXCEPTION_NOINNER(UnknownCharset, CharsetError, "charset/unknown")
 /// List of detected encodings.
 typedef std::map<float, std::string, std::greater_equal<float> > CharsetListDetected;
 
-/// @brief Return a complete list of detected character sets ordered by precidence.
+/// @brief Return a complete list of detected character sets ordered by precedence.
 /// @param file File to check
 /// @param[out] list Map to load detected list into.
-void DetectAll(const std::string file, CharsetListDetected &list);
+void DetectAll(const std::string &file, CharsetListDetected &list);
 
 /// @brief Returns the character set with the highest confidence
 /// @param file File to check
diff --git a/aegisub/libaegisub/include/libaegisub/log.h b/aegisub/libaegisub/include/libaegisub/log.h
index 6a32c10f7..ebc8a71f2 100644
--- a/aegisub/libaegisub/include/libaegisub/log.h
+++ b/aegisub/libaegisub/include/libaegisub/log.h
@@ -120,7 +120,7 @@ class LogSink {
 public:
 	/// Constructor
 	/// @param dir_log Directory to place log files.
-	LogSink(const std::string dir_log);
+	LogSink(const std::string &dir_log);
 
 	/// Destructor
 	~LogSink();