diff --git a/src/etc/rustup.sh b/src/etc/rustup.sh
index 918c0c66f76df..7c207385393c9 100755
--- a/src/etc/rustup.sh
+++ b/src/etc/rustup.sh
@@ -286,7 +286,7 @@ BOOL_OPTIONS=""
 VAL_OPTIONS=""
 
 flag uninstall "only uninstall from the installation prefix"
-valopt prefix "" "set installation prefix"
+valopt prefix "${RUSTUP_PREFIX}" "set installation prefix"
 valopt date "" "use the YYYY-MM-DD nightly instead of the current nightly"
 valopt channel "beta" "use the selected release channel [beta]"
 flag save "save the downloaded nightlies to ~/.rustup"