diff --git a/bin/df/df.1 b/bin/df/df.1
index e785321d653..9660183b033 100644
--- a/bin/df/df.1
+++ b/bin/df/df.1
@@ -71,6 +71,11 @@ Use 512-byte blocks rather than the default.  Note that
 this overrides the
 .Ev BLOCKSIZE
 specification from the environment.
+.It Fl g
+Use 1073741824-byte (1-Gbyte) blocks rather than the default.  Note that
+this overrides the
+.Ev BLOCKSIZE
+specification from the environment.
 .It Fl H
 "Human-readable" output.  Use unit suffixes: Byte, Kilobyte, Megabyte,
 Gigabyte, Terabyte and Petabyte in order to reduce the number of
diff --git a/bin/df/df.c b/bin/df/df.c
index f75b468905e..fc8cb344547 100644
--- a/bin/df/df.c
+++ b/bin/df/df.c
@@ -122,7 +122,7 @@ main(argc, argv)
 	char *mntpt, *mntpath, **vfslist;
 
 	vfslist = NULL;
-	while ((ch = getopt(argc, argv, "abHhikmnPt:")) != -1)
+	while ((ch = getopt(argc, argv, "abgHhikmnPt:")) != -1)
 		switch (ch) {
 		case 'a':
 			aflag = 1;
@@ -133,6 +133,10 @@ main(argc, argv)
 			putenv("BLOCKSIZE=512");
 			hflag = 0;
 			break;
+		case 'g':
+			putenv("BLOCKSIZE=1g");
+			hflag = 0;
+			break;
 		case 'H':
 			hflag = UNITS_SI;
 			valp = vals_si;