diff --git a/libraries/tests/rtos/mbed/semaphore/main.cpp b/libraries/tests/rtos/mbed/semaphore/main.cpp
index 2c38d453af..63b8121baf 100644
--- a/libraries/tests/rtos/mbed/semaphore/main.cpp
+++ b/libraries/tests/rtos/mbed/semaphore/main.cpp
@@ -40,7 +40,7 @@
 #elif (defined(TARGET_EFM32GG_STK3700)) && !defined(TOOLCHAIN_ARM_MICRO)
     #define STACK_SIZE 1536
 #elif defined(TARGET_MCU_NRF51822)
-    #define STACK_SIZE 512
+    #define STACK_SIZE 768
 #else
     #define STACK_SIZE DEFAULT_STACK_SIZE
 #endif