diff --git a/ext/cgi/escape/escape.c b/ext/cgi/escape/escape.c
index 77627e2f03..3a7837e4df 100644
--- a/ext/cgi/escape/escape.c
+++ b/ext/cgi/escape/escape.c
@@ -388,7 +388,7 @@ cgiesc_unescape(int argc, VALUE *argv, VALUE self)
 void
 Init_escape(void)
 {
-#if HAVE_RB_EXT_RACTOR_SAFE
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
     rb_ext_ractor_safe(true);
 #endif
 
diff --git a/ext/monitor/monitor.c b/ext/monitor/monitor.c
index 43a18f58af..00d663195f 100644
--- a/ext/monitor/monitor.c
+++ b/ext/monitor/monitor.c
@@ -203,7 +203,7 @@ monitor_synchronize(VALUE monitor)
 void
 Init_monitor(void)
 {
-#if HAVE_RB_EXT_RACTOR_SAFE
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
     rb_ext_ractor_safe(true);
 #endif
 
diff --git a/ext/racc/cparse/cparse.c b/ext/racc/cparse/cparse.c
index 8614c10e09..f71ed2bba9 100644
--- a/ext/racc/cparse/cparse.c
+++ b/ext/racc/cparse/cparse.c
@@ -819,7 +819,7 @@ reduce0(RB_BLOCK_CALL_FUNC_ARGLIST(_, data))
 void
 Init_cparse(void)
 {
-#if HAVE_RB_EXT_RACTOR_SAFE
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
     rb_ext_ractor_safe(true);
 #endif
 
diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index 45919202e4..4c5349783b 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -4564,7 +4564,7 @@ zlib_gunzip_run(VALUE arg)
 void
 Init_zlib(void)
 {
-#if HAVE_RB_EXT_RACTOR_SAFE
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
     rb_ext_ractor_safe(true);
 #endif