diff --git a/cmds-filesystem.c b/cmds-filesystem.c
index 306f7154..888e3ece 100644
--- a/cmds-filesystem.c
+++ b/cmds-filesystem.c
@@ -924,10 +924,11 @@ static int cmd_defrag(int argc, char **argv)
 }
 
 static const char * const cmd_resize_usage[] = {
-	"btrfs filesystem resize [devid:][+/-]<newsize>[gkm]|[devid:]max <path>",
+	"btrfs filesystem resize [devid:][+/-]<newsize>[kKmMgGtTpPeE]|[devid:]max <path>",
 	"Resize a filesystem",
 	"If 'max' is passed, the filesystem will occupy all available space",
 	"on the device 'devid'.",
+	"[kK] means KiB, which denotes 1KiB = 1024B, 1MiB = 1024KiB, etc.",
 	NULL
 };