diff --git a/library/gcm.c b/library/gcm.c
index d5918a5..d5761d2 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -211,7 +211,7 @@
         aesni_gcm_mult( output, x, h );
         return;
     }
-#endif
+#endif /* POLARSSL_AESNI_C && POLARSSL_HAVE_X86_64 */
 
     memset( z, 0x00, 16 );
 
@@ -924,4 +924,4 @@
 
 #endif /* POLARSSL_SELF_TEST && POLARSSL_AES_C */
 
-#endif
+#endif /* POLARSSL_GCM_C */