diff --git a/pym/_emerge/Package.py b/pym/_emerge/Package.py
index 2c1a116..cebfd82 100644
--- a/pym/_emerge/Package.py
+++ b/pym/_emerge/Package.py
@@ -3,6 +3,7 @@
 
 from __future__ import unicode_literals
 
+import functools
 import sys
 from itertools import chain
 import warnings
@@ -82,6 +83,10 @@
 
 		if eapi_attrs.iuse_effective:
 			implicit_match = self.root_config.settings._iuse_effective_match
+			if self.built:
+				implicit_match = functools.partial(
+					self._built_iuse_effective_match,
+					implicit_match, frozenset(self._metadata['USE'].split()))
 		else:
 			implicit_match = self.root_config.settings._iuse_implicit_match
 		usealiases = self.root_config.settings._use_manager.getUseAliases(self)
@@ -109,6 +114,33 @@
 			type_name=self.type_name)
 		self._hash_value = hash(self._hash_key)
 
+	@staticmethod
+	def _built_iuse_effective_match(prof_effective_match, built_use, flag):
+		"""
+		For built packages, it is desirable for the built USE setting to be
+		independent of the profile's current IUSE_IMPLICIT state, since the
+		profile's IUSE_IMPLICT setting may have diverged. Therefore, any
+		member of the built USE setting is considered to be a valid member of
+		IUSE_EFFECTIVE. Note that the binary package may be remote, so it's
+		only possible to rely on metadata that is available in the remote
+		Packages file, and the IUSE_IMPLICIT header in the Packages file is
+		vulnerable to mutation (see bug 640318).
+
+		This function is only used for EAPIs that support IUSE_EFFECTIVE,
+		since built USE settings for earlier EAPIs may contain a large
+		number of irrelevant flags.
+
+		@param prof_effective_match: function to match IUSE_EFFECTIVE
+			values for the current profile
+		@type prof_effective_match: callable
+		@param built_use: built USE setting
+		@type built_use: frozenset
+		@return: True if flag is a valid USE value which may
+			be specified in USE dependencies, False otherwise.
+		@rtype: bool
+		"""
+		return flag in built_use or prof_effective_match(flag)
+
 	@property
 	def eapi(self):
 		return self._metadata["EAPI"]
diff --git a/pym/portage/dbapi/__init__.py b/pym/portage/dbapi/__init__.py
index 9505384..2574b63 100644
--- a/pym/portage/dbapi/__init__.py
+++ b/pym/portage/dbapi/__init__.py
@@ -5,6 +5,7 @@
 
 __all__ = ["dbapi"]
 
+import functools
 import re
 
 import portage
@@ -219,6 +220,10 @@
 		eapi_attrs = _get_eapi_attrs(metadata["EAPI"])
 		if eapi_attrs.iuse_effective:
 			iuse_implicit_match = self.settings._iuse_effective_match
+			if not self._use_mutable:
+				iuse_implicit_match = functools.partial(
+					Package._built_iuse_effective_match,
+					iuse_implicit_match, frozenset(metadata["USE"].split()))
 		else:
 			iuse_implicit_match = self.settings._iuse_implicit_match
 		usealiases = self.settings._use_manager.getUseAliases(pkg)
diff --git a/pym/portage/package/ebuild/config.py b/pym/portage/package/ebuild/config.py
index cd2b009..d0225a3 100644
--- a/pym/portage/package/ebuild/config.py
+++ b/pym/portage/package/ebuild/config.py
@@ -1693,6 +1693,12 @@
 			iuse_implicit_match = self._iuse_effective_match
 			portage_iuse = set(self._iuse_effective)
 			portage_iuse.update(explicit_iuse)
+			if built_use is not None:
+				# When the binary package was built, the profile may have
+				# had different IUSE_IMPLICIT settings, so any member of
+				# the built USE setting is considered to be a member of
+				# IUSE_EFFECTIVE (see bug 640318).
+				portage_iuse.update(built_use)
 			self.configdict["pkg"]["IUSE_EFFECTIVE"] = \
 				" ".join(sorted(portage_iuse))
 		else:
diff --git a/pym/portage/tests/dbapi/test_fakedbapi.py b/pym/portage/tests/dbapi/test_fakedbapi.py
index e4f5dd7..19ea9cd 100644
--- a/pym/portage/tests/dbapi/test_fakedbapi.py
+++ b/pym/portage/tests/dbapi/test_fakedbapi.py
@@ -14,6 +14,20 @@
 
 	def testFakedbapi(self):
 		packages = (
+			("app-misc/foo-1", {
+				"EAPI"         : "2", # does not support IUSE_EFFECTIVE
+				"IUSE"         : "",
+				"repository"   : "gentoo",
+				"SLOT"         : "1",
+				"USE"          : "missing-iuse",
+			}),
+			("app-misc/foo-2", {
+				"EAPI"         : "5", # supports IUSE_EFFECTIVE
+				"IUSE"         : "",
+				"repository"   : "gentoo",
+				"SLOT"         : "2",
+				"USE"          : "missing-iuse",
+			}),
 			("sys-apps/portage-2.1.10", {
 				"EAPI"         : "2",
 				"IUSE"         : "ipc doc",
@@ -29,6 +43,12 @@
 		)
 
 		match_tests = (
+			# The missing-iuse match is only intended to work for binary
+			# packages with EAPIs that support IUSE_EFFECTIVE (bug 640318).
+			("app-misc/foo[missing-iuse]",    ["app-misc/foo-2"]),
+			("app-misc/foo[-missing-iuse]",   []),
+			("app-misc/foo",                  ["app-misc/foo-1", "app-misc/foo-2"]),
+
 			("sys-apps/portage:0[ipc]",             ["sys-apps/portage-2.1.10"]),
 			("sys-apps/portage:0[-ipc]",            []),
 			("sys-apps/portage:0[doc]",             []),