diff --git a/ext/io/console/console.c b/ext/io/console/console.c
index 7130c29a8b..2d27e1dc77 100644
--- a/ext/io/console/console.c
+++ b/ext/io/console/console.c
@@ -1071,6 +1071,9 @@ console_scroll(VALUE io, int line)
     return io;
 }
 
+#define GPERF_DOWNCASE 1
+#define GPERF_CASE_STRCMP 1
+#define gperf_case_strcmp strcasecmp
 #include "win32_vk.inc"
 
 /*
diff --git a/ext/io/console/win32_vk.inc b/ext/io/console/win32_vk.inc
index d15b1219fb..348e6be5ed 100644
--- a/ext/io/console/win32_vk.inc
+++ b/ext/io/console/win32_vk.inc
@@ -519,7 +519,7 @@ struct vktable;
 
 #ifndef GPERF_DOWNCASE
 #define GPERF_DOWNCASE 1
-static const unsigned char gperf_downcase[256] =
+static unsigned char gperf_downcase[256] =
   {
       0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,
      15,  16,  17,  18,  19,  20,  21,  22,  23,  24,  25,  26,  27,  28,  29,