diff --git a/include/spdlog/details/file_helper.h b/include/spdlog/details/file_helper.h
index 1e5ca4c6..128fe153 100644
--- a/include/spdlog/details/file_helper.h
+++ b/include/spdlog/details/file_helper.h
@@ -25,10 +25,10 @@ public:
 
     void open(const filename_t &fname, bool truncate = false);
     void reopen(bool truncate);
-    void flush();
-    void sync();
+    void flush() const;
+    void sync() const;
     void close();
-    void write(const memory_buf_t &buf);
+    void write(const memory_buf_t &buf) const;
     size_t size() const;
     const filename_t &filename() const;
 
diff --git a/include/spdlog/details/registry.h b/include/spdlog/details/registry.h
index e100c47b..30ff88ea 100644
--- a/include/spdlog/details/registry.h
+++ b/include/spdlog/details/registry.h
@@ -45,7 +45,7 @@ public:
     // This make the default API faster, but cannot be used concurrently with set_default_logger().
     // e.g do not call set_default_logger() from one thread while calling spdlog::info() from
     // another.
-    logger *get_default_raw();
+    logger *get_default_raw() const;
 
     // set default logger.
     // default logger is stored in default_logger_ (for faster retrieval) and in the loggers_ map.
diff --git a/include/spdlog/sinks/ansicolor_sink.h b/include/spdlog/sinks/ansicolor_sink.h
index 46ce2159..bc1500af 100644
--- a/include/spdlog/sinks/ansicolor_sink.h
+++ b/include/spdlog/sinks/ansicolor_sink.h
@@ -32,7 +32,7 @@ public:
 
     void set_color(level color_level, string_view_t color);
     void set_color_mode(color_mode mode);
-    bool should_color();
+    bool should_color() const;
 
     // Formatting codes
     static constexpr std::string_view reset = "\033[m";
diff --git a/include/spdlog/sinks/rotating_file_sink.h b/include/spdlog/sinks/rotating_file_sink.h
index 91b49e0f..b3011175 100644
--- a/include/spdlog/sinks/rotating_file_sink.h
+++ b/include/spdlog/sinks/rotating_file_sink.h
@@ -43,7 +43,7 @@ private:
 
     // delete the target if exists, and rename the src file  to target
     // return true on success, false otherwise.
-    bool rename_file_(const filename_t &src_filename, const filename_t &target_filename);
+    static bool rename_file_(const filename_t &src_filename, const filename_t &target_filename);
 
     filename_t base_filename_;
     std::size_t max_size_;
diff --git a/src/details/file_helper.cpp b/src/details/file_helper.cpp
index 54aa2d2a..e22bf5ed 100644
--- a/src/details/file_helper.cpp
+++ b/src/details/file_helper.cpp
@@ -62,13 +62,13 @@ void file_helper::reopen(bool truncate) {
     this->open(filename_, truncate);
 }
 
-void file_helper::flush() {
+void file_helper::flush() const {
     if (std::fflush(fd_) != 0) {
         throw_spdlog_ex("Failed flush to file " + os::filename_to_str(filename_), errno);
     }
 }
 
-void file_helper::sync() {
+void file_helper::sync() const {
     if (!os::fsync(fd_)) {
         throw_spdlog_ex("Failed to fsync file " + os::filename_to_str(filename_), errno);
     }
@@ -89,9 +89,9 @@ void file_helper::close() {
     }
 }
 
-void file_helper::write(const memory_buf_t &buf) {
+void file_helper::write(const memory_buf_t &buf) const {
     if (fd_ == nullptr) return;
-    size_t msg_size = buf.size();
+    const size_t msg_size = buf.size();
     const auto *data = buf.data();
     if (std::fwrite(data, 1, msg_size, fd_) != msg_size) {
         throw_spdlog_ex("Failed writing to file " + os::filename_to_str(filename_), errno);
diff --git a/src/details/registry.cpp b/src/details/registry.cpp
index e60c7fd1..2055b739 100644
--- a/src/details/registry.cpp
+++ b/src/details/registry.cpp
@@ -113,7 +113,7 @@ std::shared_ptr<logger> registry::default_logger() {
 // To be used directly by the spdlog default api (e.g. spdlog::info)
 // This make the default API faster, but cannot be used concurrently with set_default_logger().
 // e.g do not call set_default_logger() from one thread while calling spdlog::info() from another.
-logger *registry::get_default_raw() { return default_logger_.get(); }
+logger *registry::get_default_raw() const { return default_logger_.get(); }
 
 // set default logger.
 // default logger is stored in default_logger_ (for faster retrieval) and in the loggers_ map.
diff --git a/src/sinks/ansicolor_sink.cpp b/src/sinks/ansicolor_sink.cpp
index fe3364f0..ecac32a9 100644
--- a/src/sinks/ansicolor_sink.cpp
+++ b/src/sinks/ansicolor_sink.cpp
@@ -34,7 +34,7 @@ void ansicolor_sink<Mutex>::set_color(level color_level, string_view_t color) {
 }
 
 template <typename Mutex>
-bool ansicolor_sink<Mutex>::should_color() {
+bool ansicolor_sink<Mutex>::should_color() const {
     return should_do_colors_;
 }