diff --git a/include/polarssl/ctr_drbg.h b/include/polarssl/ctr_drbg.h
index 5a26cde..b47d389 100644
--- a/include/polarssl/ctr_drbg.h
+++ b/include/polarssl/ctr_drbg.h
@@ -224,6 +224,9 @@
  */
 int ctr_drbg_self_test( int verbose );
 
+/* Internal functions (do not call directly) */
+int ctr_drbg_init_entropy_len( ctr_drbg_context *, int (*)(void *, unsigned char *, size_t), void *, const unsigned char *, size_t, size_t );
+
 #ifdef __cplusplus
 }
 #endif