diff --git a/nanoc.gitignore b/nanoc.gitignore
index ddc964bc..4a5c90b1 100644
--- a/nanoc.gitignore
+++ b/nanoc.gitignore
@@ -5,3 +5,6 @@ output/
 
 # Temporary file directory
 tmp/
+
+# Diff file from `enable_output_diff`
+output.diff
\ No newline at end of file