diff --git a/targets/TARGET_STM/trng_api.c b/targets/TARGET_STM/trng_api.c
index cffe7a61770..f85dae2bd72 100644
--- a/targets/TARGET_STM/trng_api.c
+++ b/targets/TARGET_STM/trng_api.c
@@ -37,6 +37,15 @@ void trng_init(trng_t *obj)
         error("Only 1 RNG instance supported\r\n");
     }
 
+#if defined(TARGET_STM32L4)
+    RCC_PeriphCLKInitTypeDef PeriphClkInitStruct;
+
+    /*Select PLLQ output as RNG clock source */
+    PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_RNG;
+    PeriphClkInitStruct.RngClockSelection = RCC_RNGCLKSOURCE_PLL;
+    HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct);
+#endif
+
     /* RNG Peripheral clock enable */
     __HAL_RCC_RNG_CLK_ENABLE();