diff --git a/ChangeLog b/ChangeLog
index a6fb1e71ed..73cdbcd986 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Sun Jul 20 12:41:53 2014  Eric Wong  <e@80x24.org>
+
+	* include/ruby/io.h (rb_io_t): shrink to 200 bytes from 216 on 64-bit
+	  This puts us within 8 bytes of being three cache lines instead of
+	  four lines on x86-64.  This breaks the ABI.
+	  [Feature #10050]
+
 Sun Jul 20 12:36:46 2014  Eric Wong  <e@80x24.org>
 
 	* include/ruby/oniguruma.h (struct re_pattern_buffer): shrink to 448
diff --git a/include/ruby/io.h b/include/ruby/io.h
index 4ecd4d0b46..bdde9844e2 100644
--- a/include/ruby/io.h
+++ b/include/ruby/io.h
@@ -59,8 +59,8 @@ typedef struct {
 } rb_io_buffer_t;
 
 typedef struct rb_io_t {
-    int fd;                     /* file descriptor */
     FILE *stdio_file;		/* stdio ptr for read/write if available */
+    int fd;                     /* file descriptor */
     int mode;			/* mode flags: FMODE_XXXs */
     rb_pid_t pid;		/* child's pid (for pipes) */
     int lineno;			/* number of lines read */
@@ -89,9 +89,9 @@ typedef struct rb_io_t {
 
     rb_econv_t *writeconv;
     VALUE writeconv_asciicompat;
+    int writeconv_initialized;
     int writeconv_pre_ecflags;
     VALUE writeconv_pre_ecopts;
-    int writeconv_initialized;
 
     VALUE write_lock;
 } rb_io_t;