diff --git a/library/aes.c b/library/aes.c
index a186dee..5e01c4f 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -710,9 +710,9 @@
  * AES-ECB block encryption
  */
 #if !defined(MBEDTLS_AES_ENCRYPT_ALT)
-void mbedtls_aes_encrypt( mbedtls_aes_context *ctx,
-                          const unsigned char input[16],
-                          unsigned char output[16] )
+int mbedtls_internal_aes_encrypt( mbedtls_aes_context *ctx,
+                                  const unsigned char input[16],
+                                  unsigned char output[16] )
 {
     int i;
     uint32_t *RK, X0, X1, X2, X3, Y0, Y1, Y2, Y3;
@@ -760,6 +760,8 @@
     PUT_UINT32_LE( X1, output,  4 );
     PUT_UINT32_LE( X2, output,  8 );
     PUT_UINT32_LE( X3, output, 12 );
+
+    return( 0 );
 }
 #endif /* !MBEDTLS_AES_ENCRYPT_ALT */
 
@@ -767,9 +769,9 @@
  * AES-ECB block decryption
  */
 #if !defined(MBEDTLS_AES_DECRYPT_ALT)
-void mbedtls_aes_decrypt( mbedtls_aes_context *ctx,
-                          const unsigned char input[16],
-                          unsigned char output[16] )
+int mbedtls_internal_aes_decrypt( mbedtls_aes_context *ctx,
+                                  const unsigned char input[16],
+                                  unsigned char output[16] )
 {
     int i;
     uint32_t *RK, X0, X1, X2, X3, Y0, Y1, Y2, Y3;
@@ -817,6 +819,8 @@
     PUT_UINT32_LE( X1, output,  4 );
     PUT_UINT32_LE( X2, output,  8 );
     PUT_UINT32_LE( X3, output, 12 );
+
+    return( 0 );
 }
 #endif /* !MBEDTLS_AES_DECRYPT_ALT */
 
@@ -846,11 +850,9 @@
 #endif
 
     if( mode == MBEDTLS_AES_ENCRYPT )
-        mbedtls_aes_encrypt( ctx, input, output );
+        return( mbedtls_internal_aes_encrypt( ctx, input, output ) );
     else
-        mbedtls_aes_decrypt( ctx, input, output );
-
-    return( 0 );
+        return( mbedtls_internal_aes_decrypt( ctx, input, output ) );
 }
 
 #if defined(MBEDTLS_CIPHER_MODE_CBC)