diff --git a/lib/homebrew.sh b/lib/homebrew.sh
index e6694f8..b093d52 100755
--- a/lib/homebrew.sh
+++ b/lib/homebrew.sh
@@ -1,3 +1,8 @@
 #!/bin/sh
 
-/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
+if ! type brew > /dev/null; then
+  /usr/bin/ruby -e \
+    "$(curl \
+      -fsSL \
+      https://raw.githubusercontent.com/Homebrew/install/master/install)"
+fi