diff --git a/tools/build b/tools/build
index b3205bb..f06beae 100755
--- a/tools/build
+++ b/tools/build
@@ -2,7 +2,9 @@
 
 set -e
 
-verbose() [[ -v VERBOSE ]]
+verbose() {
+	! test -z "$VERBOSE"
+}
 
 verbose && echo "Running tests..."
 tools/test