diff --git a/include/bsd/err.h b/include/bsd/err.h
index 9e83260..adf08f6 100644
--- a/include/bsd/err.h
+++ b/include/bsd/err.h
@@ -29,11 +29,15 @@
 #include <sys/cdefs.h>
 #if __has_include_next(<err.h>)
 #include_next <err.h>
+#else
+#define LIBBSD_NEED_ERR_H_FUNCS
 #endif
 #else
 #include <bsd/sys/cdefs.h>
 #if __has_include(<err.h>)
 #include <err.h>
+#else
+#define LIBBSD_NEED_ERR_H_FUNCS
 #endif
 #endif
 
@@ -52,6 +56,26 @@ void verrc(int status, int code, const char *format, va_list ap)
 	__printflike(3, 0) __dead2;
 void errc(int status, int code, const char *format, ...)
 	__printflike(3, 4) __dead2;
+
+#ifdef LIBBSD_NEED_ERR_H_FUNCS
+void vwarn(const char *format, va_list ap)
+	__printflike(1, 0);
+void vwarnx(const char *format, va_list ap)
+	__printflike(1, 0);
+void warn(const char *format, ...)
+	__printflike(1, 2);
+void warnx(const char *format, ...)
+	__printflike(1, 2);
+
+void verr(int status, const char *format, va_list ap)
+	__printflike(2, 0) __dead2;
+void verrx(int status, const char *format, va_list ap)
+	__printflike(2, 0) __dead2;
+void err(int status, const char *format, ...)
+	__printflike(2, 3) __dead2;
+void errx(int status, const char *format, ...)
+	__printflike(2, 3) __dead2;
+#endif
 __END_DECLS
 
 #endif
diff --git a/src/err.c b/src/err.c
index 45f1b61..8f09972 100644
--- a/src/err.c
+++ b/src/err.c
@@ -26,6 +26,9 @@
  */
 
 #include <err.h>
+#ifdef LIBBSD_NEED_ERR_H_FUNCS
+#include <errno.h>
+#endif
 #include <string.h>
 #include <stdarg.h>
 #include <stdlib.h>
@@ -73,3 +76,76 @@ errc(int status, int code, const char *format, ...)
 	verrc(status, code, format, ap);
 	va_end(ap);
 }
+
+#ifdef LIBBSD_NEED_ERR_H_FUNCS
+void
+vwarn(const char *format, va_list ap)
+{
+	vwarnc(errno, format, ap);
+}
+
+void
+warn(const char *format, ...)
+{
+	va_list ap;
+
+	va_start(ap, format);
+	vwarnc(errno, format, ap);
+	va_end(ap);
+}
+
+void
+vwarnx(const char *format, va_list ap)
+{
+	fprintf(stderr, "%s: ", getprogname());
+	if (format)
+		vfprintf(stderr, format, ap);
+	fprintf(stderr, "\n");
+}
+
+void
+warnx(const char *format, ...)
+{
+	va_list ap;
+
+	va_start(ap, format);
+	vwarnx(format, ap);
+	va_end(ap);
+}
+
+void
+verr(int status, const char *format, va_list ap)
+{
+	verrc(status, errno, format, ap);
+}
+
+void
+err(int status, const char *format, ...)
+{
+	va_list ap;
+
+	va_start(ap, format);
+	verrc(status, errno, format, ap);
+	va_end(ap);
+}
+
+void
+verrx(int eval, const char *format, va_list ap)
+{
+	fprintf(stderr, "%s: ", getprogname());
+	if (format)
+		vfprintf(stderr, format, ap);
+	fprintf(stderr, "\n");
+	exit(eval);
+}
+
+void
+errx(int eval, const char *format, ...)
+{
+	va_list ap;
+
+	va_start(ap, format);
+	verrx(eval, format, ap);
+	va_end(ap);
+}
+#endif
diff --git a/src/libbsd.map b/src/libbsd.map
index ce36040..caa5cd1 100644
--- a/src/libbsd.map
+++ b/src/libbsd.map
@@ -168,3 +168,16 @@ LIBBSD_0.9.1 {
     strnvis_netbsd;
     strnunvis_netbsd;
 } LIBBSD_0.9;
+
+LIBBSD_0.10.0 {
+    /* These BSD extensions are available on GNU systems, but not on other
+     * systems such as Windows or musl libc based ones. */
+    vwarn;
+    vwarnx;
+    warn;
+    warnx;
+    verr;
+    verrx;
+    err;
+    errx;
+} LIBBSD_0.9.1;