diff --git a/collects/scribblings/reference/file-ports.scrbl b/collects/scribblings/reference/file-ports.scrbl
index 4a2b57a9fd..909fc10a6b 100644
--- a/collects/scribblings/reference/file-ports.scrbl
+++ b/collects/scribblings/reference/file-ports.scrbl
@@ -321,7 +321,8 @@ advisory on other platforms.
 
 Typically, locking is supported only for file ports, and attempting to
 acquire a lock with other kinds of file-stream ports raises an
-@racket[exn:fail:filesystem] exception.}
+@racket[exn:fail:filesystem] exception. Locking is not supported under Solaris,
+where the @racket[exn:fail:unsupported] exception is raised.}
 
 
 @defproc[(port-file-unlock [port file-stream-port?])
diff --git a/src/racket/sconfig.h b/src/racket/sconfig.h
index 8b01fd2c50..d4b0e3e916 100644
--- a/src/racket/sconfig.h
+++ b/src/racket/sconfig.h
@@ -99,6 +99,7 @@
 #  define USE_FCNTL_O_NONBLOCK
 #  define SOME_FDS_ARE_NOT_SELECTABLE
 #  define NEED_RESET_STDOUT_BLOCKING
+#  undef USE_FLOCK_FOR_FILE_LOCKS
 #  define USE_TIMEZONE_AND_ALTZONE_VAR
 #  define USE_NULL_TO_DISCONNECT_UDP
 # else
@@ -1050,6 +1051,9 @@
     pending bytes. Don't use this unless one of the HAS_<X>_IOB
     flags is used. */
 
+ /* USE_FLOCK_FOR_FILE_LOCKS means that flock() is available and works
+    for file locking. */
+
  /* CLOSE_ALL_FDS_AFTER_FORK means that all fds except 0, 1, and 2
     should be closed after performing a fork() for `process'
     and `system' calls. */
diff --git a/src/racket/src/port.c b/src/racket/src/port.c
index 4684479760..e296fd02c8 100644
--- a/src/racket/src/port.c
+++ b/src/racket/src/port.c
@@ -4694,6 +4694,7 @@ scheme_file_buffer(int argc, Scheme_Object *argv[])
 static int try_lock(int fd, int writer, int *_errid)
 {
 #ifdef UNIX_FILE_SYSTEM
+# ifdef USE_FLOCK_FOR_FILE_LOCKS
   {
     int ok;
 
@@ -4712,6 +4713,13 @@ static int try_lock(int fd, int writer, int *_errid)
     *_errid = errno;
     return 0;
   }
+# else
+  /* using fcntl(F_SETFL, ...) isn't really an option, since the
+     any-close-release-the-lock semantics of fcntl()-based locks
+     doesn't work with Racket threads that compete for a lock */
+  *_errid = ENOTSUP;
+  return 0;
+# endif
 #endif
 #ifdef WINDOWS_FILE_HANDLES
   {
@@ -4804,11 +4812,16 @@ Scheme_Object *scheme_file_unlock(int argc, Scheme_Object **argv)
   check_already_closed("port-file-unlock", argv[0]);
 
 #ifdef UNIX_FILE_SYSTEM
+# ifdef USE_FLOCK_FOR_FILE_LOCKS
   do {
     ok = flock(fd, LOCK_UN);
   } while ((ok == -1) && (errno == EINTR));
   ok = !ok;
   errid = errno;
+# else
+  ok = 0;
+  errid = ENOTSUP;
+# endif
 #endif
 #ifdef WINDOWS_FILE_HANDLES
   ok = UnlockFile((HANDLE)fd, 0, 0, LOCK_ALL_FILE_LO, LOCK_ALL_FILE_HI);
diff --git a/src/racket/uconfig.h b/src/racket/uconfig.h
index 20b0dbdffc..e7744c9b9a 100644
--- a/src/racket/uconfig.h
+++ b/src/racket/uconfig.h
@@ -14,6 +14,7 @@
 #define HAS_STANDARD_IOB
 #define FILES_HAVE_FDS
 #define USE_UNIX_SOCKETS_TCP
+#define USE_FLOCK_FOR_FILE_LOCKS
 
 #define UNIX_PROCESSES
 #define CLOSE_ALL_FDS_AFTER_FORK