diff --git a/lib/libutil/expand_number.c b/lib/libutil/expand_number.c
--- a/lib/libutil/expand_number.c
+++ b/lib/libutil/expand_number.c
@@ -33,10 +33,12 @@
 #include <ctype.h>
 #include <errno.h>
 #include <inttypes.h>
-#include <libutil.h>
 #include <stdbool.h>
 #include <stdint.h>
 
+#include <libutil.h>
+#undef expand_number
+
 int
 expand_number(const char *buf, int64_t *num)
 {
@@ -146,3 +148,19 @@
 
 	return (0);
 }
+
+int
+expand_unsigned(const char *buf, uint64_t *nump)
+{
+	int64_t num;
+	int ret;
+
+	if ((ret = expand_number(buf, &num)) < 0)
+		return (ret);
+	if (num < 0) {
+		errno = ERANGE;
+		return (-1);
+	}
+	*nump = (uint64_t)num;
+	return (0);
+}
diff --git a/lib/libutil/libutil.h b/lib/libutil/libutil.h
--- a/lib/libutil/libutil.h
+++ b/lib/libutil/libutil.h
@@ -88,7 +88,12 @@
 __BEGIN_DECLS
 void	clean_environment(const char * const *_white,
 	    const char * const *_more_white);
+int	expand_unsigned(const char *_buf, uint64_t *_num);
 int	expand_number(const char *_buf, int64_t *_num);
+#define expand_number(_buf, _num)					\
+	_Generic((_num),						\
+		 uint64_t *: expand_number_unsigned,			\
+		 default: expand_number)((_buf), (_num))
 int	extattr_namespace_to_string(int _attrnamespace, char **_string);
 int	extattr_string_to_namespace(const char *_string, int *_attrnamespace);
 int	flopen(const char *_path, int _flags, ...);