diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c9422e0d..27171b90 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -50,7 +50,7 @@ jobs:
 
       - run: rake compile
 
-      - run: rake test
+      - run: rake test JSON_COMPACT=1
 
       - run: rake build
 
@@ -78,4 +78,4 @@ jobs:
 
       - run: rake compile
 
-      - run: rake valgrind
+      - run: rake valgrind JSON_COMPACT=1
diff --git a/test/json/test_helper.rb b/test/json/test_helper.rb
index 11bb8ba8..d849e28b 100644
--- a/test/json/test_helper.rb
+++ b/test/json/test_helper.rb
@@ -3,21 +3,23 @@
 require 'json'
 require 'test/unit'
 
-if GC.respond_to?(:verify_compaction_references)
-  # This method was added in Ruby 3.0.0. Calling it this way asks the GC to
-  # move objects around, helping to find object movement bugs.
-  begin
-    GC.verify_compaction_references(expand_heap: true, toward: :empty)
-  rescue NotImplementedError, ArgumentError
-    # Some platforms don't support compaction
+if ENV["JSON_COMPACT"]
+  if GC.respond_to?(:verify_compaction_references)
+    # This method was added in Ruby 3.0.0. Calling it this way asks the GC to
+    # move objects around, helping to find object movement bugs.
+    begin
+      GC.verify_compaction_references(expand_heap: true, toward: :empty)
+    rescue NotImplementedError, ArgumentError
+      # Some platforms don't support compaction
+    end
   end
-end
 
-if GC.respond_to?(:auto_compact=)
-  begin
-    GC.auto_compact = true
-  rescue NotImplementedError
-    # Some platforms don't support compaction
+  if GC.respond_to?(:auto_compact=)
+    begin
+      GC.auto_compact = true
+    rescue NotImplementedError
+      # Some platforms don't support compaction
+    end
   end
 end