diff --git a/.github/workflows/test-external.yaml b/.github/workflows/test-external.yaml
index 3d9e373b..ae55246d 100644
--- a/.github/workflows/test-external.yaml
+++ b/.github/workflows/test-external.yaml
@@ -7,6 +7,7 @@ permissions:
 
 env:
   CONSOLE_OUTPUT: XTerm
+  RUBY_DEBUG: true
 
 jobs:
   test:
diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index 76dd8ae1..986e75d9 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -7,6 +7,7 @@ permissions:
 
 env:
   CONSOLE_OUTPUT: XTerm
+  RUBY_DEBUG: true
 
 jobs:
   test:
diff --git a/ext/extconf.rb b/ext/extconf.rb
index 8d5bfabc..b4633823 100755
--- a/ext/extconf.rb
+++ b/ext/extconf.rb
@@ -35,6 +35,10 @@
 
 $CFLAGS << " -Wall -Wno-unknown-pragmas -std=c99"
 
+if ENV.key?('RUBY_DEBUG')
+	$CFLAGS << " -DRUBY_DEBUG -O0"
+end
+
 $srcs = ["io/event/event.c", "io/event/selector/selector.c"]
 $VPATH << "$(srcdir)/io/event"
 $VPATH << "$(srcdir)/io/event/selector"