diff --git a/Dockerfile.template.erb b/Dockerfile.template.erb
index 1832d9ef..dcc3664a 100644
--- a/Dockerfile.template.erb
+++ b/Dockerfile.template.erb
@@ -116,7 +116,8 @@ RUN apt-get update \
  && export GEM_DIR=$(ruby -e 'puts Gem.dir') \
  && echo GEM_DIR=$GEM_DIR \
  && rm -rf $GEM_DIR/cache/*.gem \
- && find $GEM_DIR -type d -name test -or -name ext -or -name spec -or -name benchmark | xargs -r rm -rf \
+ # Don't purge $GEM_DIR/gems/GEM/lib/GEM/ext because it might contain runtime .so (e.g json)
+ && find $GEM_DIR -maxdepth 3 -type d -name test -or -name ext -or -name spec -or -name benchmark | xargs -r rm -rfv \
  && find $GEM_DIR -name "*.so" | xargs -r strip \
 <% if is_alpine %>
  && gem install bigdecimal -v 1.4.4 \