diff --git a/library/hmac_drbg.c b/library/hmac_drbg.c
index 1336c7e..92d7ba4 100644
--- a/library/hmac_drbg.c
+++ b/library/hmac_drbg.c
@@ -390,9 +390,13 @@
 /*
  * Set entropy length grabbed for seeding
  */
-void mbedtls_hmac_drbg_set_entropy_len( mbedtls_hmac_drbg_context *ctx, size_t len )
+int mbedtls_hmac_drbg_set_entropy_len( mbedtls_hmac_drbg_context *ctx, size_t len )
 {
+    if( len > MBEDTLS_HMAC_DRBG_MAX_INPUT )
+        return( MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG );
+
     ctx->entropy_len = len;
+    return 0;
 }
 
 /*