diff --git a/ChangeLog b/ChangeLog
index 059f0aca5..fa8b3ebdf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2014-09-24 Paulo Andrade <pcpa@gnu.org>
+
+	* lib/jit_x86-sz.c: Generate information about instruction
+	lengths for more precise calculation of buffer size on
+	Windows x64. This change is specially important because
+	the maximum instruction length is larger than other
+	systems, what could cause an out of bounds write on
+	special conditions without this update.
+
 2014-09-24 Paulo Andrade <pcpa@gnu.org>
 
 	* check/lightning.c: Add workaround to conflicting global
diff --git a/lib/jit_x86-sz.c b/lib/jit_x86-sz.c
index 2e76e0cf2..b8c9af374 100644
--- a/lib/jit_x86-sz.c
+++ b/lib/jit_x86-sz.c
@@ -350,6 +350,356 @@
 #endif /* __WORDSIZE */
 
 #if __WORDSIZE == 64
+#if __CYGWIN__
+#define JIT_INSTR_MAX 71
+    0,
+    0,
+    0,
+    0,
+    0,
+    0,
+    7,
+    71,
+    0,
+    4,
+    13,
+    6,
+    13,
+    6,
+    7,
+    6,
+    13,
+    9,
+    13,
+    9,
+    7,
+    7,
+    14,
+    20,
+    30,
+    20,
+    30,
+    22,
+    29,
+    23,
+    30,
+    25,
+    32,
+    26,
+    33,
+    22,
+    29,
+    23,
+    30,
+    6,
+    13,
+    6,
+    13,
+    6,
+    13,
+    9,
+    8,
+    9,
+    7,
+    9,
+    7,
+    6,
+    6,
+    13,
+    14,
+    13,
+    14,
+    13,
+    14,
+    13,
+    14,
+    13,
+    14,
+    13,
+    14,
+    13,
+    14,
+    13,
+    14,
+    13,
+    14,
+    13,
+    14,
+    3,
+    10,
+    7,
+    7,
+    4,
+    4,
+    3,
+    3,
+    6,
+    4,
+    15,
+    4,
+    15,
+    4,
+    15,
+    4,
+    15,
+    3,
+    14,
+    3,
+    14,
+    3,
+    14,
+    5,
+    8,
+    5,
+    8,
+    5,
+    8,
+    5,
+    8,
+    4,
+    7,
+    4,
+    6,
+    4,
+    7,
+    6,
+    17,
+    4,
+    15,
+    3,
+    14,
+    3,
+    14,
+    7,
+    7,
+    5,
+    5,
+    4,
+    6,
+    4,
+    8,
+    9,
+    10,
+    9,
+    10,
+    9,
+    13,
+    9,
+    10,
+    9,
+    19,
+    9,
+    10,
+    9,
+    10,
+    9,
+    10,
+    9,
+    10,
+    9,
+    19,
+    9,
+    13,
+    9,
+    13,
+    9,
+    10,
+    9,
+    10,
+    9,
+    10,
+    9,
+    10,
+    9,
+    10,
+    9,
+    10,
+    9,
+    10,
+    9,
+    10,
+    3,
+    5,
+    3,
+    13,
+    68,
+    0,
+    10,
+    21,
+    15,
+    21,
+    10,
+    21,
+    15,
+    21,
+    15,
+    15,
+    5,
+    16,
+    31,
+    16,
+    31,
+    18,
+    33,
+    16,
+    31,
+    16,
+    31,
+    20,
+    35,
+    16,
+    31,
+    16,
+    31,
+    16,
+    31,
+    16,
+    31,
+    16,
+    31,
+    16,
+    31,
+    16,
+    31,
+    16,
+    31,
+    5,
+    5,
+    5,
+    5,
+    5,
+    15,
+    5,
+    16,
+    6,
+    8,
+    5,
+    16,
+    6,
+    9,
+    10,
+    21,
+    10,
+    24,
+    12,
+    27,
+    10,
+    25,
+    10,
+    25,
+    13,
+    28,
+    10,
+    25,
+    10,
+    25,
+    10,
+    25,
+    10,
+    25,
+    10,
+    25,
+    10,
+    25,
+    10,
+    25,
+    10,
+    25,
+    0,
+    10,
+    25,
+    15,
+    25,
+    10,
+    25,
+    15,
+    25,
+    22,
+    16,
+    5,
+    17,
+    32,
+    17,
+    32,
+    19,
+    34,
+    17,
+    32,
+    17,
+    32,
+    21,
+    36,
+    17,
+    32,
+    17,
+    32,
+    17,
+    32,
+    17,
+    32,
+    17,
+    32,
+    17,
+    32,
+    17,
+    32,
+    17,
+    32,
+    5,
+    5,
+    5,
+    5,
+    5,
+    15,
+    5,
+    16,
+    6,
+    8,
+    5,
+    16,
+    6,
+    9,
+    11,
+    26,
+    11,
+    26,
+    13,
+    28,
+    11,
+    26,
+    11,
+    26,
+    14,
+    29,
+    11,
+    26,
+    11,
+    26,
+    11,
+    26,
+    11,
+    26,
+    11,
+    26,
+    11,
+    26,
+    11,
+    26,
+    11,
+    26,
+    0,
+    0,
+    0,
+    0,
+    0,
+    0,
+    0,
+    0,
+    0,
+    0,
+    0,
+#else
+
 #define JIT_INSTR_MAX 43
     0,
     0,
@@ -697,4 +1047,5 @@
     0,
     0,
     0,
+#endif /* __CYGWIN__ */
 #endif /* __WORDSIZE */