diff --git a/testing/SimHarness.cpp b/testing/SimHarness.cpp
index 508ac9d8..8251e517 100644
--- a/testing/SimHarness.cpp
+++ b/testing/SimHarness.cpp
@@ -69,7 +69,7 @@ void SimHarness::SetCycleTime(uint8_t millis) {
   millis_per_cycle = millis;
 }
 
-uint8_t SimHarness::CycleTime() {
+uint8_t SimHarness::CycleTime() const {
   return millis_per_cycle;
 }
 
diff --git a/testing/SimHarness.h b/testing/SimHarness.h
index f31e67fc..76fe6edb 100644
--- a/testing/SimHarness.h
+++ b/testing/SimHarness.h
@@ -35,7 +35,7 @@ class SimHarness {
   void Press(uint8_t row, uint8_t col);
   void Release(uint8_t row, uint8_t col);
   void SetCycleTime(uint8_t millis);
-  uint8_t CycleTime();
+  uint8_t CycleTime() const;
  private:
   uint8_t millis_per_cycle = 1;
 };