diff --git a/lib/curl_setup.h b/lib/curl_setup.h
index 2f566945e3..bd68d79e00 100644
--- a/lib/curl_setup.h
+++ b/lib/curl_setup.h
@@ -739,6 +739,10 @@
 #if defined(USE_WOLFSSL) && defined(USE_GNUTLS)
 /* Avoid defining unprefixed wolfSSL SHA macros colliding with nettle ones */
 #define NO_OLD_WC_NAMES
+/* Prevent wolfSSL headers including wolfssl/openssl/md4.h, to avoid its MD4_CTX
+   type clashing with the one defined via nettle/md4.h, and used in md4.c when
+   GnuTLS is enabled. */
+#define NO_MD4
 #endif
 
 /* Single point where USE_SPNEGO definition might be defined */