diff --git a/examples/platforms/nrf52811/entropy.c b/examples/platforms/nrf52811/entropy.c
index a6eff1615..0099d3269 100644
--- a/examples/platforms/nrf52811/entropy.c
+++ b/examples/platforms/nrf52811/entropy.c
@@ -37,6 +37,7 @@
 #include <openthread-core-config.h>
 #include <openthread/config.h>
 
+#include <assert.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
@@ -50,6 +51,7 @@
 static uint8_t           sBuffer[RNG_BUFFER_SIZE];
 static volatile uint32_t sReadPosition;
 static volatile uint32_t sWritePosition;
+static volatile bool     sEntropyGetEntered;
 
 static inline uint32_t bufferCount(void)
 {
@@ -176,6 +178,9 @@ otError otPlatEntropyGet(uint8_t *aOutput, uint16_t aOutputLength)
     uint8_t  copyLength;
     uint16_t index = 0;
 
+    assert(!sEntropyGetEntered);
+    sEntropyGetEntered = true;
+
     otEXPECT_ACTION(aOutput && aOutputLength, error = OT_ERROR_INVALID_ARGS);
 
     do
@@ -201,5 +206,7 @@ otError otPlatEntropyGet(uint8_t *aOutput, uint16_t aOutputLength)
     } while (index < aOutputLength);
 
 exit:
+    sEntropyGetEntered = false;
+
     return error;
 }
diff --git a/examples/platforms/nrf52840/entropy.c b/examples/platforms/nrf52840/entropy.c
index d086d270d..93c988561 100644
--- a/examples/platforms/nrf52840/entropy.c
+++ b/examples/platforms/nrf52840/entropy.c
@@ -37,6 +37,7 @@
 #include <openthread-core-config.h>
 #include <openthread/config.h>
 
+#include <assert.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
@@ -45,6 +46,8 @@
 
 #include "platform-nrf5.h"
 
+static volatile bool sEntropyGetEntered;
+
 #if SOFTDEVICE_PRESENT
 #include "softdevice.h"
 #else
@@ -193,6 +196,9 @@ otError otPlatEntropyGet(uint8_t *aOutput, uint16_t aOutputLength)
     uint8_t  copyLength;
     uint16_t index = 0;
 
+    assert(!sEntropyGetEntered);
+    sEntropyGetEntered = true;
+
     otEXPECT_ACTION(aOutput && aOutputLength, error = OT_ERROR_INVALID_ARGS);
 
     do
@@ -228,5 +234,7 @@ otError otPlatEntropyGet(uint8_t *aOutput, uint16_t aOutputLength)
     } while (index < aOutputLength);
 
 exit:
+    sEntropyGetEntered = false;
+
     return error;
 }