diff --git a/enc/encinit.c.erb b/enc/encinit.c.erb
index 70c2a1934c..120408f8e3 100644
--- a/enc/encinit.c.erb
+++ b/enc/encinit.c.erb
@@ -2,6 +2,7 @@
  * Author: yugui@google.com (Yugui Sonoda)
  */
 #include <stdio.h>
+#include "ruby.h"
 
 #define init(func, name) {	\
     extern void func(void);	\
diff --git a/enc/trans/transdb.c b/enc/trans/transdb.c
index d6ac41e967..7caf8d845d 100644
--- a/enc/trans/transdb.c
+++ b/enc/trans/transdb.c
@@ -9,6 +9,8 @@
 
 **********************************************************************/
 
+#include "ruby.h"
+
 void rb_declare_transcoder(const char *enc1, const char *enc2, const char *lib);
 
 void
diff --git a/ext/-test-/load/dot.dot/dot.dot.c b/ext/-test-/load/dot.dot/dot.dot.c
index 936d28931a..ce7563bf8d 100644
--- a/ext/-test-/load/dot.dot/dot.dot.c
+++ b/ext/-test-/load/dot.dot/dot.dot.c
@@ -1 +1,3 @@
+#include "ruby.h"
+
 void Init_dot(void) {}
diff --git a/regenc.h b/regenc.h
index 16ed6c39da..bc1365058e 100644
--- a/regenc.h
+++ b/regenc.h
@@ -51,6 +51,8 @@
 # undef ONIG_ESCAPE_UCHAR_COLLISION
 #endif
 
+#include "ruby.h"
+
 #ifdef RUBY
 # include "ruby/onigmo.h"
 #else