diff --git a/sofort/ccenv/ccenv.sh b/sofort/ccenv/ccenv.sh
index fdba47e..18dffc2 100644
--- a/sofort/ccenv/ccenv.sh
+++ b/sofort/ccenv/ccenv.sh
@@ -1440,6 +1440,19 @@ ccenv_set_os_gate_switches()
 	fi
 }
 
+ccenv_set_os_bsd_switches()
+{
+	case $ccenv_os in
+	*bsd*)
+		mb_cfgtest_headers='sys/mman.h'
+
+		if ! cfgtest_macro_definition 'MAP_ANON'; then
+			ccenv_cflags_os="${ccenv_cflags_os} -D__BSD_VISIBLE"
+		fi
+		;;
+	esac
+}
+
 ccenv_output_defs()
 {
 	ccenv_in="$mb_project_dir/sofort/ccenv/ccenv.in"
@@ -1806,6 +1819,7 @@ ccenv_set_toolchain_variables()
 	ccenv_set_os_dso_patterns
 	ccenv_set_os_pe_switches
 	ccenv_set_os_gate_switches
+	ccenv_set_os_bsd_switches
 	ccenv_set_cc_attr_visibility_vars
 
 	ccenv_output_defs
diff --git a/src/internal/slibtool_realpath_impl.c b/src/internal/slibtool_realpath_impl.c
index 4e586a8..63fc3c4 100644
--- a/src/internal/slibtool_realpath_impl.c
+++ b/src/internal/slibtool_realpath_impl.c
@@ -18,6 +18,7 @@
 
 #ifdef HAVE_SYS_SYSCALL_H
 #include <sys/syscall.h>
+#include <unistd.h>
 #endif
 
 #ifdef _MIDIPIX_ABI
@@ -28,10 +29,6 @@
 #define ENOTSUP EOPNOTSUPP
 #endif
 
-#ifdef SYS___realpathat
-extern long syscall(int, ...);
-#endif
-
 slbt_hidden int slbt_realpath(
 	int             fdat,
 	const char *    path,