diff --git a/src/p4est_io.c b/src/p4est_io.c
index 2b255ea2c..d595fe200 100644
--- a/src/p4est_io.c
+++ b/src/p4est_io.c
@@ -592,7 +592,7 @@ static int          p4est_file_error_code (int errcode, int *p4est_errcode);
 
 p4est_file_context_t *
 p4est_file_open_create (p4est_t * p4est, const char *filename,
-                        const char user_string[P4EST_FILE_USER_STRING_BYTES],
+                        const char* user_string,
                         int *errcode)
 {
   int                 mpiret, count, count_error, mpisize;
@@ -795,7 +795,7 @@ p4est_file_open_read (p4est_t * p4est, const char *filename,
 p4est_file_context_t *
 p4est_file_write_header (p4est_file_context_t * fc, size_t header_size,
                          const void *header_data,
-                         const char user_string[P4EST_FILE_USER_STRING_BYTES],
+                         const char* user_string,
                          int *errcode)
 {
   size_t              num_pad_bytes;
@@ -1167,7 +1167,7 @@ p4est_file_read_header (p4est_file_context_t * fc,
 
 p4est_file_context_t *
 p4est_file_write_field (p4est_file_context_t * fc, sc_array_t * quadrant_data,
-                        const char user_string[P4EST_FILE_USER_STRING_BYTES],
+                        const char* user_string,
                         int *errcode)
 {
   size_t              bytes_to_write, num_pad_bytes, array_size;
diff --git a/src/p4est_io.h b/src/p4est_io.h
index 61cbbdc5e..0cea2de63 100644
--- a/src/p4est_io.h
+++ b/src/p4est_io.h
@@ -218,7 +218,7 @@ p4est_file_error_t;
  */
 p4est_file_context_t *p4est_file_open_create
   (p4est_t * p4est, const char *filename,
-   const char user_string[P4EST_FILE_USER_STRING_BYTES], int *errcode);
+   const char* user_string, int *errcode);
 
 /** Open a file for reading and read its user string on rank zero.
  * The user string is broadcasted to all ranks after reading.
@@ -290,9 +290,9 @@ p4est_file_context_t *p4est_file_open_read (p4est_t * p4est,
 p4est_file_context_t *p4est_file_write_header (p4est_file_context_t * fc,
                                                size_t header_size,
                                                const void *header_data,
-                                               const char
+                                               const char*
                                                user_string
-                                               [P4EST_FILE_USER_STRING_BYTES],
+                                               ,
                                                int *errcode);
 
 /** Read a header block from an opened file.
@@ -386,9 +386,9 @@ p4est_file_context_t *p4est_file_read_header (p4est_file_context_t * fc,
  */
 p4est_file_context_t *p4est_file_write_field (p4est_file_context_t * fc,
                                               sc_array_t * quadrant_data,
-                                              const char
+                                              const char*
                                               user_string
-                                              [P4EST_FILE_USER_STRING_BYTES],
+                                              ,
                                               int *errcode);
 
 /** Read one (more) per-quadrant data set from a parallel input file.
diff --git a/src/p8est_io.h b/src/p8est_io.h
index f30e4272f..45699100e 100644
--- a/src/p8est_io.h
+++ b/src/p8est_io.h
@@ -218,7 +218,7 @@ p8est_file_error_t;
  */
 p8est_file_context_t *p8est_file_open_create
   (p8est_t * p8est, const char *filename,
-   const char user_string[P8EST_FILE_USER_STRING_BYTES], int *errcode);
+   const char* user_string, int *errcode);
 
 /** Open a file for reading and read its user string on rank zero.
  * The user string is broadcasted to all ranks after reading.
@@ -290,9 +290,9 @@ p8est_file_context_t *p8est_file_open_read (p8est_t * p8est,
 p8est_file_context_t *p8est_file_write_header (p8est_file_context_t * fc,
                                                size_t header_size,
                                                const void *header_data,
-                                               const char
+                                               const char*
                                                user_string
-                                               [P8EST_FILE_USER_STRING_BYTES],
+                                               ,
                                                int *errcode);
 
 /** Read a header block from an opened file.
@@ -386,9 +386,9 @@ p8est_file_context_t *p8est_file_read_header (p8est_file_context_t * fc,
  */
 p8est_file_context_t *p8est_file_write_field (p8est_file_context_t * fc,
                                               sc_array_t * quadrant_data,
-                                              const char
+                                              const char*
                                               user_string
-                                              [P8EST_FILE_USER_STRING_BYTES],
+                                              ,
                                               int *errcode);
 
 /** Read one (more) per-quadrant data set from a parallel input file.