diff --git a/ncdu.1 b/ncdu.1
index 1755612..0deeed7 100644
--- a/ncdu.1
+++ b/ncdu.1
@@ -286,7 +286,7 @@ when given twice it will also add
 thus ensuring that there is no way to modify the file system from within
 .Nm .
 .It Fl \-si , \-no\-si
-List sizes using base 10 prefixes, that is, powers of 1000 (KB, MB, etc), as
+List sizes using base 10 prefixes, that is, powers of 1000 (kB, MB, etc), as
 defined in the International System of Units (SI), instead of the usual base 2
 prefixes (KiB, MiB, etc).
 .It Fl \-disk\-usage , \-apparent\-size
diff --git a/src/ui.zig b/src/ui.zig
index 9aab964..2eacd26 100644
--- a/src/ui.zig
+++ b/src/ui.zig
@@ -419,7 +419,7 @@ pub const FmtSize = struct {
     pub fn fmt(v: u64) FmtSize {
         if (main.config.si) {
             if      (v < 1000)                    { return FmtSize.init("  B", v, 10, 1); }
-            else if (v < 999_950)                 { return FmtSize.init(" KB", v, 1, 100); }
+            else if (v < 999_950)                 { return FmtSize.init(" kB", v, 1, 100); }
             else if (v < 999_950_000)             { return FmtSize.init(" MB", v, 1, 100_000); }
             else if (v < 999_950_000_000)         { return FmtSize.init(" GB", v, 1, 100_000_000); }
             else if (v < 999_950_000_000_000)     { return FmtSize.init(" TB", v, 1, 100_000_000_000); }
@@ -452,11 +452,11 @@ test "fmtsize" {
     main.config.si = true;
     try FmtSize.fmt(            0).testEql("  0.0  B");
     try FmtSize.fmt(          999).testEql("999.0  B");
-    try FmtSize.fmt(         1000).testEql("  1.0 KB");
-    try FmtSize.fmt(         1049).testEql("  1.0 KB");
-    try FmtSize.fmt(         1050).testEql("  1.1 KB");
-    try FmtSize.fmt(      999_899).testEql("999.9 KB");
-    try FmtSize.fmt(      999_949).testEql("999.9 KB");
+    try FmtSize.fmt(         1000).testEql("  1.0 kB");
+    try FmtSize.fmt(         1049).testEql("  1.0 kB");
+    try FmtSize.fmt(         1050).testEql("  1.1 kB");
+    try FmtSize.fmt(      999_899).testEql("999.9 kB");
+    try FmtSize.fmt(      999_949).testEql("999.9 kB");
     try FmtSize.fmt(      999_950).testEql("  1.0 MB");
     try FmtSize.fmt(     1000_000).testEql("  1.0 MB");
     try FmtSize.fmt(  999_850_009).testEql("999.9 MB");