diff --git a/spec/ruby/optional/capi/ext/mri.h b/spec/ruby/optional/capi/ext/mri.h
index 9567990e1d..5b58310123 100644
--- a/spec/ruby/optional/capi/ext/mri.h
+++ b/spec/ruby/optional/capi/ext/mri.h
@@ -18,12 +18,10 @@
 #undef HAVE_RBIGNUM_POSITIVE_P
 #undef HAVE_RBIGNUM_NEGATIVE_P
 #undef HAVE_RB_STR_SET_LEN
-#undef HAVE_RB_STR_NEW_CSTR
 #endif
 
 #ifdef RUBY_VERSION_IS_1_8_EX_1_9
 #undef HAVE_RB_THREAD_BLOCKING_REGION
-#undef HAVE_RB_STR_NEW_CSTR
 #undef HAVE_RB_RATIONAL
 #undef HAVE_RB_RATIONAL1
 #undef HAVE_RB_RATIONAL2
diff --git a/spec/ruby/optional/capi/ext/rubyspec.h b/spec/ruby/optional/capi/ext/rubyspec.h
index c04dfe4d10..bbb930c099 100644
--- a/spec/ruby/optional/capi/ext/rubyspec.h
+++ b/spec/ruby/optional/capi/ext/rubyspec.h
@@ -199,6 +199,7 @@
 #define HAVE_RB_ENC_TO_INDEX               1
 #define HAVE_RB_OBJ_ENCODING               1
 
+#define HAVE_RB_STR_NEW_CSTR               1
 #define HAVE_RB_USASCII_STR_NEW            1
 #define HAVE_RB_USASCII_STR_NEW_CSTR       1
 #define HAVE_RB_EXTERNAL_STR_NEW           1
@@ -432,7 +433,6 @@
 #define HAVE_RB_STR_INTERN                 1
 #define HAVE_RB_STR_LEN                    1
 #define HAVE_RB_STR_NEW                    1
-#define HAVE_RB_STR_NEW_CSTR               1
 #define HAVE_RB_STR_NEW2                   1
 #define HAVE_RB_STR_NEW3                   1
 #define HAVE_RB_STR_NEW4                   1