diff --git a/array.c b/array.c
index 05fcc1c58f..dbb40db508 100644
--- a/array.c
+++ b/array.c
@@ -32,6 +32,7 @@
 #include "builtin.h"
 
 #if !ARRAY_DEBUG
+# undef NDEBUG
 # define NDEBUG
 #endif
 #include "ruby_assert.h"
diff --git a/complex.c b/complex.c
index 50f78ef1e4..2a37c42126 100644
--- a/complex.c
+++ b/complex.c
@@ -15,6 +15,7 @@
 #include <ctype.h>
 #include <math.h>
 
+#undef NDEBUG
 #define NDEBUG
 #include "id.h"
 #include "internal.h"
diff --git a/id_table.c b/id_table.c
index 4f8540246c..ade49cd8da 100644
--- a/id_table.c
+++ b/id_table.c
@@ -7,6 +7,7 @@
 #endif
 
 #if ID_TABLE_DEBUG == 0
+#undef NDEBUG
 #define NDEBUG
 #endif
 #include "ruby_assert.h"
diff --git a/rational.c b/rational.c
index b828ec1e39..f94bf921c7 100644
--- a/rational.c
+++ b/rational.c
@@ -20,6 +20,7 @@
 #include <gmp.h>
 #endif
 
+#undef NDEBUG
 #define NDEBUG
 #include "id.h"
 #include "internal.h"