diff --git a/ext/mbstring/libmbfl/config.h.vc6 b/ext/mbstring/libmbfl/config.h.vc6
index aaa5a5c2992..9379061dff4 100644
--- a/ext/mbstring/libmbfl/config.h.vc6
+++ b/ext/mbstring/libmbfl/config.h.vc6
@@ -11,4 +11,3 @@
 #define USE_WIN32_NATIVE_THREAD 1
 #define ENABLE_THREADS 1
 
-#define strcasecmp(s1, s2) stricmp(s1, s2)
diff --git a/ext/mbstring/libmbfl/mbfl/mbfl_allocators.c b/ext/mbstring/libmbfl/mbfl/mbfl_allocators.c
index be9d345b061..697e6c79192 100644
--- a/ext/mbstring/libmbfl/mbfl/mbfl_allocators.c
+++ b/ext/mbstring/libmbfl/mbfl/mbfl_allocators.c
@@ -29,7 +29,7 @@
  */
 
 #ifdef HAVE_CONFIG_H
-#include "config.h"
+#include "../config.h"
 #endif
 
 #ifdef HAVE_STDLIB_H
diff --git a/ext/mbstring/libmbfl/mbfl/mbfl_compat.h b/ext/mbstring/libmbfl/mbfl/mbfl_compat.h
new file mode 100644
index 00000000000..0197e9047d6
--- /dev/null
+++ b/ext/mbstring/libmbfl/mbfl/mbfl_compat.h
@@ -0,0 +1,3 @@
+#ifndef HAVE_STRCASECMP
+#define strcasecmp(s1, s2) stricmp(s1, s2)
+#endif
diff --git a/ext/mbstring/libmbfl/mbfl/mbfl_convert.c b/ext/mbstring/libmbfl/mbfl/mbfl_convert.c
index 2b9090eb59e..17629d10e4c 100644
--- a/ext/mbstring/libmbfl/mbfl/mbfl_convert.c
+++ b/ext/mbstring/libmbfl/mbfl/mbfl_convert.c
@@ -29,7 +29,7 @@
  */
 
 #ifdef HAVE_CONFIG_H
-#include "config.h"
+#include "../config.h"
 #endif
 
 #ifdef HAVE_STDDEF_H
diff --git a/ext/mbstring/libmbfl/mbfl/mbfl_encoding.c b/ext/mbstring/libmbfl/mbfl/mbfl_encoding.c
index a30a8f38101..07b94d6f6dc 100644
--- a/ext/mbstring/libmbfl/mbfl/mbfl_encoding.c
+++ b/ext/mbstring/libmbfl/mbfl/mbfl_encoding.c
@@ -44,6 +44,7 @@
 #include <strings.h>
 #endif
 
+#include "mbfl_compat.h"
 #include "mbfl_encoding.h"
 #include "mbfilter_pass.h"
 #include "mbfilter_8bit.h"
diff --git a/ext/mbstring/libmbfl/mbfl/mbfl_language.c b/ext/mbstring/libmbfl/mbfl/mbfl_language.c
index 2a8146b84f0..0f7e612fef1 100644
--- a/ext/mbstring/libmbfl/mbfl/mbfl_language.c
+++ b/ext/mbstring/libmbfl/mbfl/mbfl_language.c
@@ -50,6 +50,7 @@
 
 #include "mbfl_encoding.h"
 #include "mbfl_language.h"
+#include "mbfl_compat.h"
 
 #include "nls/nls_ja.h"
 #include "nls/nls_kr.h"