diff --git a/drupalci.cs-only.yml b/drupalci.cs-only.yml
index 1c61f02..710dd94 100644
--- a/drupalci.cs-only.yml
+++ b/drupalci.cs-only.yml
@@ -10,5 +10,9 @@ build:
       eslint:
         halt-on-fail: false
       phpcs:
-        # phpcs will use core's specified version of Coder.
+        # Setting sniff-all-files to false will make the testbot either sniff
+        # only modified files, or all files if there aren't any modified ones.
+        # Setting it to true will make the testbot always sniff all files.
+        # Defaults to false.
+        sniff-all-files: true
         halt-on-fail: false
diff --git a/drupalci.yml b/drupalci.yml
index 1c61f02..710dd94 100644
--- a/drupalci.yml
+++ b/drupalci.yml
@@ -10,5 +10,9 @@ build:
       eslint:
         halt-on-fail: false
       phpcs:
-        # phpcs will use core's specified version of Coder.
+        # Setting sniff-all-files to false will make the testbot either sniff
+        # only modified files, or all files if there aren't any modified ones.
+        # Setting it to true will make the testbot always sniff all files.
+        # Defaults to false.
+        sniff-all-files: true
         halt-on-fail: false