diff --git a/Makefile b/Makefile
index 9f60a13..9d1293a 100644
--- a/Makefile
+++ b/Makefile
@@ -56,6 +56,7 @@ LIBUTILSRC =\
 	libutil/md5.c\
 	libutil/mkdirp.c\
 	libutil/mode.c\
+	libutil/parseoffset.c\
 	libutil/putword.c\
 	libutil/reallocarray.c\
 	libutil/recurse.c\
diff --git a/libutil/parseoffset.c b/libutil/parseoffset.c
new file mode 100644
index 0000000..451d913
--- /dev/null
+++ b/libutil/parseoffset.c
@@ -0,0 +1,59 @@
+/* See LICENSE file for copyright and license details. */
+#include <ctype.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "../util.h"
+
+off_t
+parseoffset(const char *str)
+{
+	off_t res;
+	size_t scale;
+	int base = 10;
+	char *end;
+
+	/* bases */
+	if (!strncasecmp(str, "0x", strlen("0x"))) {
+		base = 16;
+	} else if (*str == '0') {
+		str++;
+		base = 8;
+	}
+
+	res = strtol(str, &end, base);
+	if (res < 0) {
+		weprintf("invalid file offset: %s\n", str);
+		return -1;
+	}
+
+	/* suffix */
+	if (*end) {
+		switch (toupper((int)*end)) {
+		case 'B':
+			scale = 512L;
+			break;
+		case 'K':
+			scale = 1024L;
+			break;
+		case 'M':
+			scale = 1024L * 1024L;
+			break;
+		case 'G':
+			scale = 1024L * 1024L * 1024L;
+			break;
+		default:
+			weprintf("invalid file offset suffix: %s\n", str);
+			return -1;
+		}
+	}
+
+	/* prevent overflow */
+	if (res > (SIZE_MAX / scale)) {
+		weprintf("file offset out of range: %s\n", str);
+		return -1;
+	}
+
+	return res;
+}
diff --git a/util.h b/util.h
index b0bf0f4..4c973d1 100644
--- a/util.h
+++ b/util.h
@@ -68,6 +68,7 @@ void fnck(const char *, const char *, int (*)(const char *, const char *, int),
 mode_t getumask(void);
 char *humansize(off_t);
 mode_t parsemode(const char *, mode_t, mode_t);
+off_t parseoffset(const char *);
 void putword(FILE *, const char *);
 #undef strtonum
 long long strtonum(const char *, long long, long long, const char **);