Index: secure/lib/libcrypto/Makefile
===================================================================
--- secure/lib/libcrypto/Makefile
+++ secure/lib/libcrypto/Makefile
@@ -121,6 +121,11 @@
 SRCS+=	bn_asm.c
 .endif
 
+# Full of strict aliasing violations that LLVM has been seen to break with
+# optimisations, which can lead to ECDSA signatures not working. See
+# https://github.com/openssl/openssl/issues/12247 for the upstream bug report.
+CFLAGS.bn_nist.c+=	-fno-strict-aliasing
+
 # buffer
 SRCS+=	buf_err.c buffer.c