diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index 3815dc7..48efada 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -56,10 +56,6 @@
     ctx->reseed_counter = -1;
 
     ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
-
-#if defined(MBEDTLS_THREADING_C)
-    mbedtls_mutex_init( &ctx->mutex );
-#endif
 }
 
 /*
@@ -72,15 +68,13 @@
         return;
 
 #if defined(MBEDTLS_THREADING_C)
-    mbedtls_mutex_free( &ctx->mutex );
+    if( ctx->f_entropy != NULL )
+        mbedtls_mutex_free( &ctx->mutex );
 #endif
     mbedtls_aes_free( &ctx->aes_ctx );
     mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ctr_drbg_context ) );
     ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
     ctx->reseed_counter = -1;
-#if defined(MBEDTLS_THREADING_C)
-    mbedtls_mutex_init( &ctx->mutex );
-#endif
 }
 
 void mbedtls_ctr_drbg_set_prediction_resistance( mbedtls_ctr_drbg_context *ctx,
@@ -464,6 +458,10 @@
 
     memset( key, 0, MBEDTLS_CTR_DRBG_KEYSIZE );
 
+#if defined(MBEDTLS_THREADING_C)
+    mbedtls_mutex_init( &ctx->mutex );
+#endif
+
     mbedtls_aes_init( &ctx->aes_ctx );
 
     ctx->f_entropy = f_entropy;