diff --git a/src/core/common/random_manager.cpp b/src/core/common/random_manager.cpp
index d5962cddd..c9602bded 100644
--- a/src/core/common/random_manager.cpp
+++ b/src/core/common/random_manager.cpp
@@ -65,17 +65,17 @@ RandomManager::RandomManager(void)
 
 #ifndef OPENTHREAD_RADIO
     sEntropy.Init();
-#endif
+    sCtrDrbg.Init();
 
+    error = Random::Crypto::FillBuffer(reinterpret_cast<uint8_t *>(&seed), sizeof(seed));
+    assert(error == OT_ERROR_NONE);
+#else
     error = otPlatEntropyGet(reinterpret_cast<uint8_t *>(&seed), sizeof(seed));
     assert(error == OT_ERROR_NONE);
+#endif
 
     sPrng.Init(seed);
 
-#ifndef OPENTHREAD_RADIO
-    sCtrDrbg.Init();
-#endif
-
 exit:
     sInitCount++;
 }