diff --git a/rcl/include/rcl/timer.h b/rcl/include/rcl/timer.h
index 2403e2c32..5aa10b4a1 100644
--- a/rcl/include/rcl/timer.h
+++ b/rcl/include/rcl/timer.h
@@ -319,7 +319,7 @@ rcl_timer_call_with_info(rcl_timer_t * timer, rcl_timer_call_info_t * call_info)
 RCL_PUBLIC
 RCL_WARN_UNUSED
 rcl_ret_t
-rcl_timer_clock(rcl_timer_t * timer, rcl_clock_t ** clock);
+rcl_timer_clock(const rcl_timer_t * timer, rcl_clock_t ** clock);
 
 /// Calculates whether or not the timer should be called.
 /**
diff --git a/rcl/src/rcl/timer.c b/rcl/src/rcl/timer.c
index 4eacbc8d3..cf9acda5d 100644
--- a/rcl/src/rcl/timer.c
+++ b/rcl/src/rcl/timer.c
@@ -254,7 +254,7 @@ rcl_timer_fini(rcl_timer_t * timer)
 RCL_PUBLIC
 RCL_WARN_UNUSED
 rcl_ret_t
-rcl_timer_clock(rcl_timer_t * timer, rcl_clock_t ** clock)
+rcl_timer_clock(const rcl_timer_t * timer, rcl_clock_t ** clock)
 {
   RCL_CHECK_ARGUMENT_FOR_NULL(timer, RCL_RET_INVALID_ARGUMENT);
   RCL_CHECK_ARGUMENT_FOR_NULL(clock, RCL_RET_INVALID_ARGUMENT);