diff --git a/externals/Makefile.am b/externals/Makefile.am
index 32357d2066..467fd9e8f2 100644
--- a/externals/Makefile.am
+++ b/externals/Makefile.am
@@ -11,6 +11,7 @@ $(DB).tar.gz:
 
 $(DB): $(DB).tar.gz
 	gunzip < $(srcdir)/$(DB).tar.gz | tar xvf -
+	cd $(DB) && patch -p1 < $(srcdir)/bdb-cygwin.patch
 
 have-db:
 	$(MAKE) $(DB)
@@ -100,7 +101,7 @@ endif
 
 all: build-db build-aterm build-bzip2
 
-EXTRA_DIST = $(DB).tar.gz $(ATERM).tar.gz $(BZIP2).tar.gz
+EXTRA_DIST = $(DB).tar.gz $(ATERM).tar.gz $(BZIP2).tar.gz bdb-cygwin.patch
 
 ext-clean:
 	$(RM) -f have-db build-db have-aterm build-aterm
diff --git a/externals/bdb-cygwin.patch b/externals/bdb-cygwin.patch
new file mode 100644
index 0000000000..3f9d658b5d
--- /dev/null
+++ b/externals/bdb-cygwin.patch
@@ -0,0 +1,21 @@
+diff -rc db-4.4.20.NC-old/os/os_flock.c db-4.4.20.NC/os/os_flock.c
+*** db-4.4.20.NC-old/os/os_flock.c	Mon Jun 20 16:59:01 2005
+--- db-4.4.20.NC/os/os_flock.c	Wed Jun  7 17:01:49 2006
+***************
+*** 36,41 ****
+--- 36,50 ----
+  
+  	DB_ASSERT(F_ISSET(fhp, DB_FH_OPENED) && fhp->fd != -1);
+  
++ #ifdef __CYGWIN__
++ 	/*
++ 	 * Windows file locking interferes with read/write operations, so we
++ 	 * map the ranges to an area past the end of the file.
++ 	 */
++ 	DB_ASSERT(offset < (off_t) 1 << 62);
++ 	offset += (off_t) 1 << 62;
++ #endif
++ 
+  #ifdef HAVE_FCNTL
+  	fl.l_start = offset;
+  	fl.l_len = 1;