diff --git a/README.adoc b/README.adoc
index 46251ab..b8e805c 100644
--- a/README.adoc
+++ b/README.adoc
@@ -4014,6 +4014,23 @@ If you modify the userland programs, rebuild simply with:
 ./build-userland
 ....
 
+To rebuild just QEMU userland if you hack it, use:
+
+....
+./build-qemu --mode userland
+....
+
+The:
+
+....
+--mode userland
+....
+
+is needed because QEMU has two separate executables:
+
+* `qemu-x86_64` for userland
+* `qemu-system-x86_64` for full system
+
 ==== User mode GDB
 
 It's nice when <<gdb,the obvious>> just works, right?