Apparently, Linux is identified with __linux__ as well.
diff --git a/e_os2.h b/e_os2.h
index 18b6852..ea92ff5 100644
--- a/e_os2.h
+++ b/e_os2.h
@@ -144,7 +144,7 @@
 
 /* --------------------------------- Unix ---------------------------------- */
 #ifdef OPENSSL_SYS_UNIX
-# if defined(linux) || defined(OPENSSL_SYSNAME_LINUX)
+# if defined(linux) || defined(__linux__) || defined(OPENSSL_SYSNAME_LINUX)
 #  define OPENSSL_SYS_LINUX
 # endif
 # ifdef OPENSSL_SYSNAME_MPE