diff --git a/mysql-test/r/mysqld--defaults-file.result b/mysql-test/r/mysqld--defaults-file.result
new file mode 100644
index 00000000000..5fd5ca8d95a
--- /dev/null
+++ b/mysql-test/r/mysqld--defaults-file.result
@@ -0,0 +1,12 @@
+Could not open required defaults file: /path/with/no/extension
+Fatal error in defaults handling. Program aborted
+Could not open required defaults file: /path/with.ext
+Fatal error in defaults handling. Program aborted
+Could not open required defaults file: MYSQL_TEST_DIR/relative/path/with.ext
+Fatal error in defaults handling. Program aborted
+Could not open required defaults file: MYSQL_TEST_DIR/relative/path/without/extension
+Fatal error in defaults handling. Program aborted
+Could not open required defaults file: MYSQL_TEST_DIR/with.ext
+Fatal error in defaults handling. Program aborted
+Could not open required defaults file: MYSQL_TEST_DIR/no_extension
+Fatal error in defaults handling. Program aborted
diff --git a/mysql-test/t/mysqld--defaults-file.test b/mysql-test/t/mysqld--defaults-file.test
new file mode 100644
index 00000000000..065436c38aa
--- /dev/null
+++ b/mysql-test/t/mysqld--defaults-file.test
@@ -0,0 +1,47 @@
+# BUG#58455
+# Starting mysqld with defaults file without extension cause
+# segmentation fault
+
+source include/not_embedded.inc;
+source include/not_windows.inc;
+
+# We need to use a plain "mysqld" without any other options to trigger
+# the bug. In particular, it seems that passing --bootstrap does not
+# trigger the bug. To do that, we extract the "command name" from the
+# MYSQLD_BOOTSTRAP_CMD variable and store that in a file, which we
+# then load into the test case.
+
+perl;
+  my ($mysqld)= split " ", $ENV{MYSQLD_BOOTSTRAP_CMD};
+  open(FILE, ">", "$ENV{MYSQL_TMP_DIR}/mysqld.inc") or die;
+  print FILE "let \$MYSQLD= $mysqld;\n";
+  close FILE;
+EOF
+
+source $MYSQL_TMP_DIR/mysqld.inc;
+
+# All these tests refer to configuration files that do not exist
+
+--error 1
+exec $MYSQLD --defaults-file=/path/with/no/extension --print-defaults 2>&1;
+
+--error 1
+exec $MYSQLD --defaults-file=/path/with.ext --print-defaults 2>&1;
+
+--replace_result $MYSQL_TEST_DIR MYSQL_TEST_DIR
+--error 1
+exec $MYSQLD --defaults-file=relative/path/with.ext --print-defaults 2>&1;
+
+--replace_result $MYSQL_TEST_DIR MYSQL_TEST_DIR
+--error 1
+exec $MYSQLD --defaults-file=relative/path/without/extension --print-defaults 2>&1;
+
+--replace_result $MYSQL_TEST_DIR MYSQL_TEST_DIR
+--error 1
+exec $MYSQLD --defaults-file=with.ext --print-defaults 2>&1;
+
+--replace_result $MYSQL_TEST_DIR MYSQL_TEST_DIR
+--error 1
+exec $MYSQLD --defaults-file=no_extension --print-defaults 2>&1;
+
+remove_file $MYSQL_TMP_DIR/mysqld.inc;
diff --git a/mysys/default.c b/mysys/default.c
index 432c3086254..9a4b990f003 100644
--- a/mysys/default.c
+++ b/mysys/default.c
@@ -179,7 +179,7 @@ fn_expand(const char *filename, char *result_buf)
   if (my_getwd(dir, sizeof(dir), MYF(0)))
     DBUG_RETURN(3);
   DBUG_PRINT("debug", ("dir: %s", dir));
-  if (fn_format(result_buf, filename, dir, NULL, flags) == NULL)
+  if (fn_format(result_buf, filename, dir, "", flags) == NULL)
     DBUG_RETURN(2);
   DBUG_PRINT("return", ("result: %s", result_buf));
   DBUG_RETURN(0);
diff --git a/mysys/mf_format.c b/mysys/mf_format.c
index 6afa2938fa3..74f114a966f 100644
--- a/mysys/mf_format.c
+++ b/mysys/mf_format.c
@@ -31,6 +31,8 @@ char * fn_format(char * to, const char *name, const char *dir,
   reg1 size_t length;
   size_t dev_length;
   DBUG_ENTER("fn_format");
+  DBUG_ASSERT(name != NULL);
+  DBUG_ASSERT(extension != NULL);
   DBUG_PRINT("enter",("name: %s  dir: %s  extension: %s  flag: %d",
 		       name,dir,extension,flag));