diff --git a/TESTS/mbed_hal/lp_us_tickers/main.cpp b/TESTS/mbed_hal/lp_us_tickers/main.cpp
index 5e1ced8af1..a0283e17b0 100644
--- a/TESTS/mbed_hal/lp_us_tickers/main.cpp
+++ b/TESTS/mbed_hal/lp_us_tickers/main.cpp
@@ -49,8 +49,10 @@ unsigned int ticker_overflow_delta;
 
 /* Auxiliary function to count ticker ticks elapsed during execution of N cycles of empty while loop.
  * Parameter <step> is used to disable compiler optimisation. */
-uint32_t count_ticks(volatile uint32_t cycles, uint32_t step)
+uint32_t count_ticks(uint32_t cycles, uint32_t step)
 {
+    register uint32_t reg_cycles = cycles;
+
     core_util_critical_section_enter();
 
     const uint32_t start = intf->read();