diff --git a/core/themes/classy/classy.info.yml b/core/themes/classy/classy.info.yml
index fb5cb3e..bd47945 100644
--- a/core/themes/classy/classy.info.yml
+++ b/core/themes/classy/classy.info.yml
@@ -5,6 +5,7 @@ package: Core
 version: VERSION
 core: 8.x
 base theme: false
+hidden: true

 libraries:
   - classy/base
diff --git a/core/themes/stable/stable.info.yml b/core/themes/stable/stable.info.yml
index 687c434..960a683 100644
--- a/core/themes/stable/stable.info.yml
+++ b/core/themes/stable/stable.info.yml
@@ -5,3 +5,4 @@ package: Core
 version: VERSION
 core: 8.x
 base theme: false
+hidden: true