diff --git a/src/df.c b/src/df.c
index 01ecca6..8941632 100644
--- a/src/df.c
+++ b/src/df.c
@@ -1276,7 +1276,7 @@ or all file systems by default.\n\
       fputs (_("\
   -a, --all             include dummy file systems\n\
   -B, --block-size=SIZE  scale sizes by SIZE before printing them; e.g.,\n\
-                           '-BM' prints sizes in units of 1,048,576 bytes;\n\
+                           '-BMiB' prints sizes in units of 1,048,576 bytes;\n\
                            see SIZE format below\n\
       --total           produce a grand total\n\
   -h, --human-readable  print sizes in powers of 1024 (e.g., 1023M)\n\
diff --git a/src/du.c b/src/du.c
index 890edb6..215cb21 100644
--- a/src/du.c
+++ b/src/du.c
@@ -299,7 +299,7 @@ Summarize disk usage of each FILE, recursively for directories.\n\
 "), stdout);
       fputs (_("\
   -B, --block-size=SIZE  scale sizes by SIZE before printing them; e.g.,\n\
-                           '-BM' prints sizes in units of 1,048,576 bytes;\n\
+                           '-BMiB' prints sizes in units of 1,048,576 bytes;\n\
                            see SIZE format below\n\
   -b, --bytes           equivalent to '--apparent-size --block-size=1'\n\
   -c, --total           produce a grand total\n\
diff --git a/src/ls.c b/src/ls.c
index 25e10fa..6f5fef7 100644
--- a/src/ls.c
+++ b/src/ls.c
@@ -4793,7 +4793,7 @@ Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.\n\
 "), stdout);
       fputs (_("\
       --block-size=SIZE      scale sizes by SIZE before printing them; e.g.,\n\
-                               '--block-size=M' prints sizes in units of\n\
+                               '--block-size=MiB' prints sizes in units of\n\
                                1,048,576 bytes; see SIZE format below\n\
   -B, --ignore-backups       do not list implied entries ending with ~\n\
   -c                         with -lt: sort by, and show, ctime (time of last\n\