diff --git a/library/bignum.c b/library/bignum.c
index e555692..110c3f4 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1301,7 +1301,7 @@
             r0 -= m;
 
             Z.p[i - t - 1] = ( q1 << biH ) | q0;
-#endif
+#endif /* POLARSSL_HAVE_UDBL && !64-bit Apple with Clang 5.0 */
         }
 
         Z.p[i - t - 1]++;
diff --git a/library/net.c b/library/net.c
index 0866149..8ccf120 100644
--- a/library/net.c
+++ b/library/net.c
@@ -62,7 +62,7 @@
 
 static int wsa_init_done = 0;
 
-#else
+#else /* ( _WIN32 || _WIN32_WCE ) && !EFIX64 && !EFI32 */
 
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -91,7 +91,7 @@
 #include <endian.h>
 #endif
 
-#endif
+#endif /* ( _WIN32 || _WIN32_WCE ) && !EFIX64 && !EFI32 */
 
 #include <stdlib.h>
 #include <stdio.h>
@@ -409,7 +409,7 @@
     }
     return( 0 );
 }
-#endif
+#endif /* ( _WIN32 || _WIN32_WCE ) && !EFIX64 && !EFI32 */
 
 /*
  * Accept a connection from a remote client
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index cd207c5..03b8010 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -2340,7 +2340,7 @@
             }
         }
         else
-#endif
+#endif /* POLARSSL_SSL_PROTO_TLS1_2 */
 #if defined(POLARSSL_SSL_PROTO_SSL3) || defined(POLARSSL_SSL_PROTO_TLS1) || \
     defined(POLARSSL_SSL_PROTO_TLS1_1)
         if ( ciphersuite_info->key_exchange ==
diff --git a/library/x509.c b/library/x509.c
index adb025c..73e1347 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -592,7 +592,7 @@
         *sig_opts = (void *) pss_opts;
     }
     else
-#endif
+#endif /* POLARSSL_X509_RSASSA_PSS_SUPPORT */
     {
         /* Make sure parameters are absent or NULL */
         if( ( sig_params->tag != ASN1_NULL && sig_params->tag != 0 ) ||