diff --git a/storage/mroonga/udf/mrn_udf_command.cpp b/storage/mroonga/udf/mrn_udf_command.cpp
index 46911c56e25..44d8c9ccdd0 100644
--- a/storage/mroonga/udf/mrn_udf_command.cpp
+++ b/storage/mroonga/udf/mrn_udf_command.cpp
@@ -220,7 +220,7 @@ static void mroonga_command_escape_value(grn_ctx *ctx,
 }
 
 MRN_API char *mroonga_command(UDF_INIT *init, UDF_ARGS *args, char *result,
-                              unsigned long *length, char *is_null, char *error)
+                              unsigned long *length, uchar *is_null, uchar *error)
 {
   CommandInfo *info = (CommandInfo *)init->ptr;
   grn_ctx *ctx = info->ctx;
diff --git a/storage/mroonga/udf/mrn_udf_escape.cpp b/storage/mroonga/udf/mrn_udf_escape.cpp
index 55a3639565e..a03bf25cba2 100644
--- a/storage/mroonga/udf/mrn_udf_escape.cpp
+++ b/storage/mroonga/udf/mrn_udf_escape.cpp
@@ -214,7 +214,7 @@ static void escape(EscapeInfo *info, UDF_ARGS *args)
 }
 
 MRN_API char *mroonga_escape(UDF_INIT *init, UDF_ARGS *args, char *result,
-                             unsigned long *length, char *is_null, char *error)
+                             unsigned long *length, uchar *is_null, uchar *error)
 {
   EscapeInfo *info = reinterpret_cast<EscapeInfo *>(init->ptr);
   grn_ctx *ctx = info->ctx;
diff --git a/storage/mroonga/udf/mrn_udf_highlight_html.cpp b/storage/mroonga/udf/mrn_udf_highlight_html.cpp
index d986777caff..5085a885fe0 100644
--- a/storage/mroonga/udf/mrn_udf_highlight_html.cpp
+++ b/storage/mroonga/udf/mrn_udf_highlight_html.cpp
@@ -412,8 +412,8 @@ MRN_API char *mroonga_highlight_html(UDF_INIT *init,
                                      UDF_ARGS *args,
                                      char *result,
                                      unsigned long *length,
-                                     char *is_null,
-                                     char *error)
+                                     uchar *is_null,
+                                     uchar *error)
 {
   MRN_DBUG_ENTER_FUNCTION();
 
diff --git a/storage/mroonga/udf/mrn_udf_last_insert_grn_id.cpp b/storage/mroonga/udf/mrn_udf_last_insert_grn_id.cpp
index f40dcf0055f..fb948a72ea9 100644
--- a/storage/mroonga/udf/mrn_udf_last_insert_grn_id.cpp
+++ b/storage/mroonga/udf/mrn_udf_last_insert_grn_id.cpp
@@ -45,7 +45,7 @@ MRN_API my_bool last_insert_grn_id_init(UDF_INIT *init, UDF_ARGS *args, char *me
   return 0;
 }
 
-MRN_API longlong last_insert_grn_id(UDF_INIT *init, UDF_ARGS *args, char *is_null, char *error)
+MRN_API longlong last_insert_grn_id(UDF_INIT *init, UDF_ARGS *args, uchar *is_null, uchar *error)
 {
   THD *thd = current_thd;
   st_mrn_slot_data *slot_data = mrn_get_slot_data(thd, false);
diff --git a/storage/mroonga/udf/mrn_udf_normalize.cpp b/storage/mroonga/udf/mrn_udf_normalize.cpp
index 0ebee2ff608..5c34e9b0ec7 100644
--- a/storage/mroonga/udf/mrn_udf_normalize.cpp
+++ b/storage/mroonga/udf/mrn_udf_normalize.cpp
@@ -151,7 +151,7 @@ error:
 }
 
 MRN_API char *mroonga_normalize(UDF_INIT *init, UDF_ARGS *args, char *result,
-                                unsigned long *length, char *is_null, char *error)
+                                unsigned long *length, uchar *is_null, uchar *error)
 {
   st_mrn_normalize_info *info = (st_mrn_normalize_info *)init->ptr;
   grn_ctx *ctx = info->ctx;
diff --git a/storage/mroonga/udf/mrn_udf_query_expand.cpp b/storage/mroonga/udf/mrn_udf_query_expand.cpp
index 76a5dad53b4..4ecafe1812b 100644
--- a/storage/mroonga/udf/mrn_udf_query_expand.cpp
+++ b/storage/mroonga/udf/mrn_udf_query_expand.cpp
@@ -244,8 +244,8 @@ MRN_API char *mroonga_query_expand(UDF_INIT *init,
                                    UDF_ARGS *args,
                                    char *result,
                                    unsigned long *length,
-                                   char *is_null,
-                                   char *error)
+                                   uchar *is_null,
+                                   uchar *error)
 {
   MRN_DBUG_ENTER_FUNCTION();
 
diff --git a/storage/mroonga/udf/mrn_udf_snippet.cpp b/storage/mroonga/udf/mrn_udf_snippet.cpp
index 1bd6cb7d722..53058bf02f5 100644
--- a/storage/mroonga/udf/mrn_udf_snippet.cpp
+++ b/storage/mroonga/udf/mrn_udf_snippet.cpp
@@ -248,7 +248,7 @@ error:
 }
 
 MRN_API char *mroonga_snippet(UDF_INIT *init, UDF_ARGS *args, char *result,
-                              unsigned long *length, char *is_null, char *error)
+                              unsigned long *length, uchar *is_null, uchar *error)
 {
   st_mrn_snip_info *snip_info = (st_mrn_snip_info *) init->ptr;
   grn_ctx *ctx = snip_info->ctx;
diff --git a/storage/mroonga/udf/mrn_udf_snippet_html.cpp b/storage/mroonga/udf/mrn_udf_snippet_html.cpp
index ba0cdadda99..3acdef03f54 100644
--- a/storage/mroonga/udf/mrn_udf_snippet_html.cpp
+++ b/storage/mroonga/udf/mrn_udf_snippet_html.cpp
@@ -323,8 +323,8 @@ MRN_API char *mroonga_snippet_html(UDF_INIT *init,
                                    UDF_ARGS *args,
                                    char *result,
                                    unsigned long *length,
-                                   char *is_null,
-                                   char *error)
+                                   uchar *is_null,
+                                   uchar *error)
 {
   MRN_DBUG_ENTER_FUNCTION();