diff --git a/BUILDING.md b/BUILDING.md
index a7b91fc40ee5..0062c5da4a59 100644
--- a/BUILDING.md
+++ b/BUILDING.md
@@ -978,8 +978,8 @@ that works for both your host and target environments.
 
 You can find other ICU releases at
 [the ICU homepage](https://icu.unicode.org/download).
-Download the file named something like `icu4c-**##.#**-src.tgz` (or
-`.zip`).
+Download the source archive named something like
+`icu4c-**##.#**-sources.tgz` (or `.zip`).
 
 To check the minimum recommended ICU, run `./configure --help` and see
 the help for the `--with-icu-source` option. A warning will be printed
@@ -987,12 +987,15 @@ during configuration if the ICU version is too old.
 
 #### Unix/macOS
 
-From an already-unpacked ICU:
+From an already-unpacked ICU source archive:
 
 ```bash
 ./configure --with-intl=[small-icu,full-icu] --with-icu-source=/path/to/icu
 ```
 
+(Simply cloning the icu4c repository will not work here; the source directory
+must have been unpacked from the compiled `-sources` archive.)
+
 From a local ICU tarball:
 
 ```bash
@@ -1008,7 +1011,7 @@ From a tarball URL:
 #### Windows
 
 First unpack latest ICU to `deps/icu`
-[icu4c-**##.#**-src.tgz](https://icu.unicode.org/download) (or `.zip`)
+[icu4c-**##.#**-sources.tgz](https://icu.unicode.org/download) (or `.zip`)
 as `deps/icu` (You'll have: `deps/icu/source/...`)
 
 ```powershell