diff --git a/lib/compat.c b/lib/compat.c
index 02527dbd..a36cebd9 100644
--- a/lib/compat.c
+++ b/lib/compat.c
@@ -206,8 +206,8 @@ char *do_big_num(int64 num, int human_flag, const char *fract)
 				break;
 		}
 
-		snprintf(bufs[n], sizeof bufs[0], "%.*f%c", precision,
-			(double) num / powi, *units);
+		snprintf(bufs[n], sizeof bufs[0], "%.*f%c%s", precision,
+			(double) num / powi, *units, num > mult && mult == 1024 ? "i" : "");
 		return bufs[n];
 	}
 
diff --git a/rsync.1.md b/rsync.1.md
index a593c1cd..fbdfd480 100644
--- a/rsync.1.md
+++ b/rsync.1.md
@@ -3312,6 +3312,8 @@ expand it.
     (mega), `G` (giga), `T` (tera), `P` (peta), `E` (exa), `Z` (zetta) or `Y`
     (yotta). For example, a 1234567-byte file would output as 1.23M in level-2
     (assuming that a period is your local decimal point).
+    Additionally an `i` is appended in level-3 to indicate the binary base.
+    The same file would output as 1.17Mi in level-3.
 
     Backward compatibility note: versions of rsync prior to 3.1.0 do not
     support human-readable level 1, and they default to level 0.  Thus,