diff --git a/libraries/AP_RPM/AP_RPM.cpp b/libraries/AP_RPM/AP_RPM.cpp
index 5976860bdb..11c1bd89e8 100644
--- a/libraries/AP_RPM/AP_RPM.cpp
+++ b/libraries/AP_RPM/AP_RPM.cpp
@@ -282,7 +282,7 @@ bool AP_RPM::arming_checks(size_t buflen, char *buffer) const
 }
 
 #if HAL_LOGGING_ENABLED
-void AP_RPM::Log_RPM()
+void AP_RPM::Log_RPM() const
 {
     float rpm1 = -1, rpm2 = -1;
 
diff --git a/libraries/AP_RPM/AP_RPM.h b/libraries/AP_RPM/AP_RPM.h
index baaf9d1d1f..bc66c7937f 100644
--- a/libraries/AP_RPM/AP_RPM.h
+++ b/libraries/AP_RPM/AP_RPM.h
@@ -118,7 +118,7 @@ private:
 
     void detect_instance(uint8_t instance);
 
-    void Log_RPM();
+    void Log_RPM() const;
 };
 
 namespace AP {