diff --git a/src/Sender.cpp b/src/Sender.cpp
index cc0fc47..a9fcab9 100644
--- a/src/Sender.cpp
+++ b/src/Sender.cpp
@@ -251,7 +251,7 @@ void Sender::resumeFor(int n, void (*doneTXFunc)(Sender *s)) {
   enableIRQs();
 }
 
-bool Sender::isTransmitting() {
+bool Sender::isTransmitting() const {
   // Check these both atomically
   disableIRQs();
   //{
diff --git a/src/TeensyDMX.h b/src/TeensyDMX.h
index 18c9593..8b2d2f3 100644
--- a/src/TeensyDMX.h
+++ b/src/TeensyDMX.h
@@ -482,7 +482,7 @@ class Sender final : public TeensyDMX {
   // Returns whether we are currently paused. This will occur after pause()
   // is called and after any "resumed" messages are sent. Note that it is
   // possible that a packet is still in the middle of being transmitted.
-  bool isPaused() {
+  bool isPaused() const {
     return paused_;
   }
 
@@ -527,7 +527,7 @@ class Sender final : public TeensyDMX {
   //
   // An alternative to this function is to use onDoneTransmitting to be
   // notified when transmission is complete.
-  bool isTransmitting();
+  bool isTransmitting() const;
 
   // Sets the function to call when the sender is paused and transmission
   // of the current packet is done. This can be used instead of polling