With a more modern 64-bit MS compiler, I still get a failure. I see that Cygwin released theirs, so I'm guessing this is a MS compiler issue. cl /Fotmp32dll\cversion.obj -Iinc32 -Itmp32dll /MD /Ox -DOPENSSL_THREADS -DDSO_WIN32 -W3 -Gs0 -Gy -nologo -DOPENSSL_SYSNAME_WIN32 -DWIN32_LEAN_AND_MEAN -DL_ENDIAN -DUNICODE -D_UNICODE -D_CRT_SECURE_NO_DEPRECATE -DOPENSSL_IA32_SSE2 -DOPENSSL_BN_ASM_MONT -DOPENSSL_BN_ASM_MONT5 -DOPENSSL_BN_ASM_GF2m -DSHA1_ASM -DSHA256_ASM -DSHA512_ASM -DMD5_ASM -DAES_ASM -DVPAES_ASM -DBSAES_ASM -DWHIRLPOOL_ASM -DGHASH_ASM -DOPENSSL_USE_APPLINK -I. -DOPENSSL_NO_RC5 -DOPENSSL_NO_MD2 -DOPENSSL_NO_KRB5 -DOPENSSL_NO_JPAKE -DOPENSSL_NO_STATIC_ENGINE /Zi /Fdtmp32dll/lib -D_WINDLL -DOPENSSL_BUILD_SHLIBCRYPTO -DMK1MF_BUILD -DMK1MF_PLATFORM_VC_WIN64A -c .\crypto\cversion.c cversion.c crypto\cversion.c(80) : error C2065: 'cflags' : undeclared identifier crypto\cversion.c(80) : warning C4047: 'return' : 'const char *' differs in levels of indirection from 'int' NMAKE : fatal error U1077: 'cl' : return code '0x2' Stop. Microsoft (R) C/C++ Optimizing Compiler Version 14.00.40310.41 for AMD64 and the same Microsoft Platform SDK for Windows Server 2003 R2. Help? Thanks.