diff --git a/INSTALL.md b/INSTALL.md
index 7a8a3bd91..5cae9c1d4 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -34,6 +34,10 @@ Please refer to instructions provided by the repository.
 
 - lablgtk3 and its prerequisites (ocamlfind, GTK 3 and its dependencies)
 
+##### Optional, on BSDs
+
+- libinotify (optional, for building unison-fsmonitor)
+
 ##### Optional, for building the user manual
 
 - LaTeX
diff --git a/src/Makefile.OCaml b/src/Makefile.OCaml
index a0e12b2c8..1662c9ab5 100644
--- a/src/Makefile.OCaml
+++ b/src/Makefile.OCaml
@@ -324,6 +324,20 @@ ifeq ($(OSARCH),Linux)
   FSMDIR = fsmonitor/inotify
 endif
 
+ifneq ($(findstring $(OSARCH),FreeBSD OpenBSD NetBSD DragonFly),)
+  LIBINOTIFY_LIB:=-cclib '$(shell pkg-config --libs libinotify 2> /dev/null || printf ' -linotify')'
+  LIBINOTIFY_INC:=-ccopt '$(shell pkg-config --cflags libinotify 2> /dev/null)'
+  FOUND_LIBINOTIFY := $(shell { printf '' > inotifytest__.ml ;\
+    $(CAMLC) $(CAMLCFLAGS) $(CAMLLDFLAGS) $(LIBINOTIFY_LIB) \
+      -o inotifytest__ inotifytest__.ml > /dev/null 2>&1 && printf true ; } ;\
+    rm -f inotifytest__.ml inotifytest__.cm[oix] inotifytest__.o inotifytest__ > /dev/null 2>&1)
+  ifeq ($(FOUND_LIBINOTIFY), true)
+    FSMDIR = fsmonitor/inotify
+    $(NAME_FSM)$(EXEC_EXT): CAMLCFLAGS += $(LIBINOTIFY_INC)
+    $(NAME_FSM)$(EXEC_EXT): CLIBS += $(LIBINOTIFY_LIB)
+  endif
+endif
+
 ifeq ($(OSARCH),SunOS)
   FSMDIR = fsmonitor/solaris
 endif