--- a/explain/syscall/ustat.c
+++ b/explain/syscall/ustat.c
@@ -30,7 +30,7 @@
 #include <explain/syscall/ustat.h>
 
 
-#ifndef HAVE_USTAT
+#if !defined(HAVE_USTAT_H) && !defined(LINUX_TYPES_H_STRUCT_USTAT)
 
 struct ustat
 {
--- a/libexplain/buffer/enfile.c
+++ b/libexplain/buffer/enfile.c
@@ -38,7 +38,7 @@ get_maxfile(void)
 {
     if (explain_option_dialect_specific())
     {
-#ifdef __linux__
+#ifdef SYS__sysctl
         /*
          * In the linux kernel, if get_empty_filp() returns NULL, the open
          * system call (and others) will return ENFILE.
--- a/libexplain/buffer/errno/listen.c
+++ b/libexplain/buffer/errno/listen.c
@@ -72,7 +72,7 @@ append_getsockname(explain_string_buffer_t *sb, int fildes)
 static int
 get_somaxconn(void)
 {
-#ifdef __linux__
+#ifdef SYS__sysctl
     struct __sysctl_args args;
     long somaxconn;
     size_t somaxconn_size = sizeof(somaxconn);