diff --git a/pkgs/development/libraries/db4/db4-4.5.nix b/pkgs/development/libraries/db4/db4-4.5.nix
index b55a7cfc4c0..c67deaeda45 100644
--- a/pkgs/development/libraries/db4/db4-4.5.nix
+++ b/pkgs/development/libraries/db4/db4-4.5.nix
@@ -11,5 +11,5 @@ stdenv.mkDerivation {
     (if cxxSupport then "--enable-cxx" else "--disable-cxx")
     (if compat185 then "--enable-compat185" else "--disable-compat185")
   ];
-  patches = [./cygwin-4.5.patch];
+  patches = [./cygwin-4.5.patch ./register-race-fix.patch];
 }
diff --git a/pkgs/development/libraries/db4/register-race-fix.patch b/pkgs/development/libraries/db4/register-race-fix.patch
new file mode 100644
index 00000000000..bb05c966e5b
--- /dev/null
+++ b/pkgs/development/libraries/db4/register-race-fix.patch
@@ -0,0 +1,47 @@
+diff -rc db-4.5.20-orig/env/env_register.c db-4.5.20/env/env_register.c
+*** db-4.5.20-orig/env/env_register.c	2006-09-09 16:29:04.000000000 +0200
+--- db-4.5.20/env/env_register.c	2007-05-16 21:13:27.000000000 +0200
+***************
+*** 255,260 ****
+--- 255,262 ----
+  			buf[nr - 1] = '\0';
+  		}
+  
++                 //sleep(3);
++ 
+  		pos = (off_t)lcnt * PID_LEN;
+  		if (REGISTRY_LOCK(dbenv, pos, 1) == 0) {
+  			if ((ret = REGISTRY_UNLOCK(dbenv, pos)) != 0)
+***************
+*** 361,366 ****
+--- 363,392 ----
+  	if (recovery_failed)
+  		goto err;
+  
++         //sleep(5);
++ 
++         /*
++          * Acquire an exclusive lock to prevent a race like this:
++          *
++          * 1) Process X is about to exit and process Y is just
++          *    starting.
++          * 2) Process Y reads X's slot.
++          * 3) Process X clears its slot.
++          * 4) Process Y sees that X's slot isn't cleared yet (since it
++          *    just read the old value).
++          * 5) Process X closes the registry, releases the lock on its
++          *    slot.
++          * 6) Process Y tries to acquire X's slot and succeeds, so it
++          *    concludes that X died and recovery is needed.
++          *
++          * A more efficient solution to this problem would be to let
++          * __envreg_add acquire the lock on a slot first, and *then*
++          * read the slot (instead of the other way around).  Then we
++          * wouldn't need the exclusive lock here.
++          */
++ 	if ((ret = REGISTRY_EXCL_LOCK(dbenv, 0)) != 0)
++ 		goto err;
++ 
+  	/*
+  	 * Why isn't an exclusive lock necessary to discard a DB_ENV handle?
+  	 *