diff --git a/libraries/AP_Logger/AP_Logger.cpp b/libraries/AP_Logger/AP_Logger.cpp
index ce0a994fa8..bf31bb794c 100644
--- a/libraries/AP_Logger/AP_Logger.cpp
+++ b/libraries/AP_Logger/AP_Logger.cpp
@@ -1114,7 +1114,7 @@ AP_Logger::log_write_fmt *AP_Logger::msg_fmt_for_name(const char *name, const ch
     return f;
 }
 
-const struct LogStructure *AP_Logger::structure_for_msg_type(const uint8_t msg_type)
+const struct LogStructure *AP_Logger::structure_for_msg_type(const uint8_t msg_type) const
 {
     for (uint16_t i=0; i<_num_types;i++) {
         const struct LogStructure *s = structure(i);
diff --git a/libraries/AP_Logger/AP_Logger.h b/libraries/AP_Logger/AP_Logger.h
index 5ba0a8e5ad..7f06a9b147 100644
--- a/libraries/AP_Logger/AP_Logger.h
+++ b/libraries/AP_Logger/AP_Logger.h
@@ -497,7 +497,7 @@ private:
     // return (possibly allocating) a log_write_fmt for a name
     const struct log_write_fmt *log_write_fmt_for_msg_type(uint8_t msg_type) const;
 
-    const struct LogStructure *structure_for_msg_type(uint8_t msg_type);
+    const struct LogStructure *structure_for_msg_type(uint8_t msg_type) const;
 
     // return a msg_type which is not currently in use (or -1 if none available)
     int16_t find_free_msg_type() const;
@@ -588,7 +588,7 @@ private:
     // can be used by other subsystems to detect if they should log data
     uint8_t _log_start_count;
 
-    bool should_handle_log_message();
+    bool should_handle_log_message() const;
     void handle_log_message(class GCS_MAVLINK &, const mavlink_message_t &msg);
 
     void handle_log_request_list(class GCS_MAVLINK &, const mavlink_message_t &msg);
diff --git a/libraries/AP_Logger/AP_Logger_Backend.cpp b/libraries/AP_Logger/AP_Logger_Backend.cpp
index 190274f59c..261d019ea0 100644
--- a/libraries/AP_Logger/AP_Logger_Backend.cpp
+++ b/libraries/AP_Logger/AP_Logger_Backend.cpp
@@ -44,7 +44,7 @@ const struct MultiplierStructure *AP_Logger_Backend::multiplier(uint8_t num) con
     return _front.multiplier(num);
 }
 
-AP_Logger_Backend::vehicle_startup_message_Writer AP_Logger_Backend::vehicle_message_writer() {
+AP_Logger_Backend::vehicle_startup_message_Writer AP_Logger_Backend::vehicle_message_writer() const {
     return _front._vehicle_messages;
 }
 
diff --git a/libraries/AP_Logger/AP_Logger_Backend.h b/libraries/AP_Logger/AP_Logger_Backend.h
index dcbcde6eef..6d583a0047 100644
--- a/libraries/AP_Logger/AP_Logger_Backend.h
+++ b/libraries/AP_Logger/AP_Logger_Backend.h
@@ -15,7 +15,7 @@ public:
     AP_Logger_Backend(AP_Logger &front,
                       class LoggerMessageWriter_DFLogStart *writer);
 
-    vehicle_startup_message_Writer vehicle_message_writer();
+    vehicle_startup_message_Writer vehicle_message_writer() const;
 
     virtual bool CardInserted(void) const = 0;
 
diff --git a/libraries/AP_Logger/AP_Logger_Block.cpp b/libraries/AP_Logger/AP_Logger_Block.cpp
index ca60652d6e..8457d532b8 100644
--- a/libraries/AP_Logger/AP_Logger_Block.cpp
+++ b/libraries/AP_Logger/AP_Logger_Block.cpp
@@ -261,7 +261,7 @@ void AP_Logger_Block::StartLogFile(uint16_t FileNumber)
     df_Write_FilePage = 1;
 }
 
-uint16_t AP_Logger_Block::GetFileNumber()
+uint16_t AP_Logger_Block::GetFileNumber() const
 {
     return df_FileNumber;
 }
diff --git a/libraries/AP_Logger/AP_Logger_Block.h b/libraries/AP_Logger/AP_Logger_Block.h
index d91cebb3e8..0eb723629c 100644
--- a/libraries/AP_Logger/AP_Logger_Block.h
+++ b/libraries/AP_Logger/AP_Logger_Block.h
@@ -41,12 +41,12 @@ protected:
     bool WritesOK() const override;
 
     // get the current sector from the current page
-    uint32_t get_sector(uint32_t current_page) {
+    uint32_t get_sector(uint32_t current_page) const {
         return ((current_page - 1) / df_PagePerSector);
     }
 
     // get the current block from the current page
-    uint32_t get_block(uint32_t current_page) {
+    uint32_t get_block(uint32_t current_page) const {
         return ((current_page - 1) / df_PagePerBlock);
     }
 
@@ -154,7 +154,7 @@ private:
 
     void StartLogFile(uint16_t FileNumber);
     // file numbers
-    uint16_t GetFileNumber();
+    uint16_t GetFileNumber() const;
 
     void _print_log_formats(AP_HAL::BetterStream *port);
 
diff --git a/libraries/AP_Logger/AP_Logger_MAVLink.cpp b/libraries/AP_Logger/AP_Logger_MAVLink.cpp
index 58fc3c2420..952352b379 100644
--- a/libraries/AP_Logger/AP_Logger_MAVLink.cpp
+++ b/libraries/AP_Logger/AP_Logger_MAVLink.cpp
@@ -54,7 +54,7 @@ uint32_t AP_Logger_MAVLink::bufferspace_available() {
     return (_blockcount_free * 200 + remaining_space_in_current_block());
 }
 
-uint8_t AP_Logger_MAVLink::remaining_space_in_current_block() {
+uint8_t AP_Logger_MAVLink::remaining_space_in_current_block() const {
     // note that _current_block *could* be NULL ATM.
     return (MAVLINK_MSG_REMOTE_LOG_DATA_BLOCK_FIELD_DATA_LEN - _latest_block_len);
 }
diff --git a/libraries/AP_Logger/AP_Logger_MAVLink.h b/libraries/AP_Logger/AP_Logger_MAVLink.h
index 3df7afd92d..d1a74430d5 100644
--- a/libraries/AP_Logger/AP_Logger_MAVLink.h
+++ b/libraries/AP_Logger/AP_Logger_MAVLink.h
@@ -145,7 +145,7 @@ private:
     void Write_logger_MAV(AP_Logger_MAVLink &logger);
 
     uint32_t bufferspace_available() override; // in bytes
-    uint8_t remaining_space_in_current_block();
+    uint8_t remaining_space_in_current_block() const;
     // write buffer
     uint8_t _blockcount_free;
     uint8_t _blockcount;
diff --git a/libraries/AP_Logger/AP_Logger_MAVLinkLogTransfer.cpp b/libraries/AP_Logger/AP_Logger_MAVLinkLogTransfer.cpp
index 6c119091d9..5a099b2d67 100644
--- a/libraries/AP_Logger/AP_Logger_MAVLinkLogTransfer.cpp
+++ b/libraries/AP_Logger/AP_Logger_MAVLinkLogTransfer.cpp
@@ -25,7 +25,7 @@
 extern const AP_HAL::HAL& hal;
 
 // We avoid doing log messages when timing is critical:
-bool AP_Logger::should_handle_log_message()
+bool AP_Logger::should_handle_log_message() const
 {
     if (!WritesEnabled()) {
         // this is currently used as a proxy for "in_mavlink_delay"
diff --git a/libraries/AP_Logger/LoggerMessageWriter.h b/libraries/AP_Logger/LoggerMessageWriter.h
index 6bf967d4fa..0744d1f96e 100644
--- a/libraries/AP_Logger/LoggerMessageWriter.h
+++ b/libraries/AP_Logger/LoggerMessageWriter.h
@@ -92,8 +92,8 @@ public:
 
     void reset() override;
     void process() override;
-    bool fmt_done() { return _fmt_done; }
-    bool params_done() { return _params_done; }
+    bool fmt_done() const { return _fmt_done; }
+    bool params_done() const { return _params_done; }
 
     // reset some writers so we push stuff out to logs again.  Will
     // only work if we are in state DONE!