diff --git a/yamllint/rules/indentation.py b/yamllint/rules/indentation.py
index 7964cdf..55b2985 100644
--- a/yamllint/rules/indentation.py
+++ b/yamllint/rules/indentation.py
@@ -38,7 +38,7 @@ Use this rule to control the indentation.
 
  rules:
    indentation:
-     spaces: consistent
+     spaces: 'consistent'
      indent-sequences: true
      check-multi-line-strings: false