diff --git a/library/hmac_drbg.c b/library/hmac_drbg.c
index aa3e251..25a0225 100644
--- a/library/hmac_drbg.c
+++ b/library/hmac_drbg.c
@@ -53,6 +53,8 @@
 {
     memset( ctx, 0, sizeof( mbedtls_hmac_drbg_context ) );
 
+    ctx->reseed_interval = MBEDTLS_HMAC_DRBG_RESEED_INTERVAL;
+
 #if defined(MBEDTLS_THREADING_C)
     mbedtls_mutex_init( &ctx->mutex );
 #endif
@@ -266,8 +268,6 @@
     ctx->f_entropy = f_entropy;
     ctx->p_entropy = p_entropy;
 
-    ctx->reseed_interval = MBEDTLS_HMAC_DRBG_RESEED_INTERVAL;
-
     if( ctx->entropy_len == 0 )
     {
         /*
@@ -412,7 +412,8 @@
 }
 
 /*
- * Free an HMAC_DRBG context
+ *  This function resets HMAC_DRBG context to the state immediately
+ *  after initial call of mbedtls_hmac_drbg_init().
  */
 void mbedtls_hmac_drbg_free( mbedtls_hmac_drbg_context *ctx )
 {
@@ -424,6 +425,10 @@
 #endif
     mbedtls_md_free( &ctx->md_ctx );
     mbedtls_platform_zeroize( ctx, sizeof( mbedtls_hmac_drbg_context ) );
+    ctx->reseed_interval = MBEDTLS_HMAC_DRBG_RESEED_INTERVAL;
+#if defined(MBEDTLS_THREADING_C)
+    mbedtls_mutex_init( &ctx->mutex );
+#endif
 }
 
 #if defined(MBEDTLS_FS_IO)