diff --git a/src/Composer/Installer.php b/src/Composer/Installer.php
index 992a7c69f..897e67d56 100644
--- a/src/Composer/Installer.php
+++ b/src/Composer/Installer.php
@@ -325,6 +325,20 @@ class Installer
         // creating requirements request
         $request = $this->createRequest($pool, $this->package, $platformRepo);
 
+        if (!$installFromLock) {
+            // remove unstable packages from the localRepo if they don't match the current stability settings
+            $removedUnstablePackages = array();
+            foreach ($localRepo->getPackages() as $package) {
+                if (
+                    !$pool->isPackageAcceptable($package->getName(), $package->getStability())
+                    && $this->installationManager->isPackageInstalled($localRepo, $package)
+                ) {
+                    $removedUnstablePackages[$package->getName()] = true;
+                    $request->remove($package->getName(), new VersionConstraint('=', $package->getVersion()));
+                }
+            }
+        }
+
         if ($this->update) {
             $this->io->write('<info>Updating dependencies'.($withDevReqs?' (including require-dev)':'').'</info>');
 
@@ -339,6 +353,43 @@ class Installer
             foreach ($links as $link) {
                 $request->install($link->getTarget(), $link->getConstraint());
             }
+
+            // if the updateWhitelist is enabled, packages not in it are also fixed
+            // to the version specified in the lock, or their currently installed version
+            if ($this->updateWhitelist) {
+                if ($this->locker->isLocked()) {
+                    try {
+                        $currentPackages = $this->locker->getLockedRepository($withDevReqs)->getPackages();
+                    } catch (\RuntimeException $e) {
+                        // fetch only non-dev packages from lock if doing a dev update fails due to a previously incomplete lock file
+                        $currentPackages = $this->locker->getLockedRepository()->getPackages();
+                    }
+                } else {
+                    $currentPackages = $installedRepo->getPackages();
+                }
+
+                // collect packages to fixate from root requirements as well as installed packages
+                $candidates = array();
+                foreach ($links as $link) {
+                    $candidates[$link->getTarget()] = true;
+                }
+                foreach ($localRepo->getPackages() as $package) {
+                    $candidates[$package->getName()] = true;
+                }
+
+                // fix them to the version in lock (or currently installed) if they are not updateable
+                foreach ($candidates as $candidate => $dummy) {
+                    foreach ($currentPackages as $curPackage) {
+                        if ($curPackage->getName() === $candidate) {
+                            if (!$this->isUpdateable($curPackage) && !isset($removedUnstablePackages[$curPackage->getName()])) {
+                                $constraint = new VersionConstraint('=', $curPackage->getVersion());
+                                $request->install($curPackage->getName(), $constraint);
+                            }
+                            break;
+                        }
+                    }
+                }
+            }
         } elseif ($installFromLock) {
             $this->io->write('<info>Installing dependencies'.($withDevReqs?' (including require-dev)':'').' from lock file</info>');
 
@@ -377,44 +428,6 @@ class Installer
             }
         }
 
-        // if the updateWhitelist is enabled, packages not in it are also fixed
-        // to the version specified in the lock, or their currently installed version
-        if ($this->update && $this->updateWhitelist) {
-            if ($this->locker->isLocked()) {
-                try {
-                    $currentPackages = $this->locker->getLockedRepository($withDevReqs)->getPackages();
-                } catch (\RuntimeException $e) {
-                    // fetch only non-dev packages from lock if doing a dev update fails due to a previously incomplete lock file
-                    $currentPackages = $this->locker->getLockedRepository()->getPackages();
-                }
-            } else {
-                $currentPackages = $installedRepo->getPackages();
-            }
-
-            // collect links from composer as well as installed packages
-            $candidates = array();
-            foreach ($links as $link) {
-                $candidates[$link->getTarget()] = true;
-            }
-            foreach ($localRepo->getPackages() as $package) {
-                $candidates[$package->getName()] = true;
-            }
-
-            // fix them to the version in lock (or currently installed) if they are not updateable
-            foreach ($candidates as $candidate => $dummy) {
-                foreach ($currentPackages as $curPackage) {
-                    if ($curPackage->getName() === $candidate) {
-                        if ($this->isUpdateable($curPackage)) {
-                            break;
-                        }
-
-                        $constraint = new VersionConstraint('=', $curPackage->getVersion());
-                        $request->install($curPackage->getName(), $constraint);
-                    }
-                }
-            }
-        }
-
         // force dev packages to have the latest links if we update or install from a (potentially new) lock
         $this->processDevPackages($localRepo, $pool, $policy, $repositories, $lockedRepository, $installFromLock, 'force-links');
 
@@ -512,9 +525,7 @@ class Installer
         $constraint->setPrettyString($rootPackage->getPrettyVersion());
         $request->install($rootPackage->getName(), $constraint);
 
-        // fix the version of all installed packages (+ platform) that are not
-        // in the current local repo to prevent rogue updates (e.g. non-dev
-        // updating when in dev)
+        // fix the version of all platform packages to prevent the solver trying to remove those
         foreach ($platformRepo->getPackages() as $package) {
             $constraint = new VersionConstraint('=', $package->getVersion());
             $constraint->setPrettyString($package->getPrettyVersion());
diff --git a/tests/Composer/Test/Fixtures/installer/partial-update-downgrades-non-whitelisted-unstable.test b/tests/Composer/Test/Fixtures/installer/partial-update-downgrades-non-whitelisted-unstable.test
new file mode 100644
index 000000000..fb618ebe3
--- /dev/null
+++ b/tests/Composer/Test/Fixtures/installer/partial-update-downgrades-non-whitelisted-unstable.test
@@ -0,0 +1,65 @@
+--TEST--
+Partial update from lock file should apply lock file and downgrade unstable packages even if not whitelisted
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                { "name": "a/old", "version": "1.0.0" },
+                { "name": "a/old", "version": "2.0.0" },
+                { "name": "b/unstable", "version": "1.0.0" },
+                { "name": "b/unstable", "version": "1.1.0-alpha" },
+                { "name": "c/uptodate", "version": "1.0.0" },
+                { "name": "d/removed", "version": "1.0.0" }
+            ]
+        }
+    ],
+    "require": {
+        "a/old": "*",
+        "b/unstable": "*",
+        "c/uptodate": "*"
+    }
+}
+--LOCK--
+{
+    "packages": [
+        { "name": "a/old", "version": "1.0.0" },
+        { "name": "b/unstable", "version": "1.1.0-alpha" },
+        { "name": "c/uptodate", "version": "1.0.0" },
+        { "name": "d/removed", "version": "1.0.0" }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": {
+        "b/unstable": 15
+    },
+    "platform": [],
+    "platform-dev": []
+}
+--INSTALLED--
+[
+    { "name": "a/old", "version": "0.9.0" },
+    { "name": "b/unstable", "version": "1.1.0-alpha" },
+    { "name": "c/uptodate", "version": "2.0.0" }
+]
+--RUN--
+update c/uptodate
+--EXPECT-LOCK--
+{
+    "packages": [
+        { "name": "a/old", "version": "1.0.0", "type": "library" },
+        { "name": "b/unstable", "version": "1.0.0", "type": "library" },
+        { "name": "c/uptodate", "version": "2.0.0", "type": "library" }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": [],
+    "platform": [],
+    "platform-dev": []
+}
+--EXPECT--
+Updating a/old (0.9.0) to a/old (1.0.0)
+Updating b/unstable (1.1.0-alpha) to b/unstable (1.0.0)
diff --git a/tests/Composer/Test/Fixtures/installer/partial-update-from-lock.test b/tests/Composer/Test/Fixtures/installer/partial-update-from-lock.test
new file mode 100644
index 000000000..51368b861
--- /dev/null
+++ b/tests/Composer/Test/Fixtures/installer/partial-update-from-lock.test
@@ -0,0 +1,66 @@
+--TEST--
+Partial update from lock file should update everything to the state of the lock, remove overly unstable packages
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                { "name": "a/old", "version": "1.0.0" },
+                { "name": "a/old", "version": "2.0.0" },
+                { "name": "b/unstable", "version": "1.0.0" },
+                { "name": "b/unstable", "version": "1.1.0-alpha" },
+                { "name": "c/uptodate", "version": "1.0.0" },
+                { "name": "d/removed", "version": "1.0.0" }
+            ]
+        }
+    ],
+    "require": {
+        "a/old": "*",
+        "b/unstable": "*",
+        "c/uptodate": "*"
+    }
+}
+--LOCK--
+{
+    "packages": [
+        { "name": "a/old", "version": "1.0.0" },
+        { "name": "b/unstable", "version": "1.1.0-alpha" },
+        { "name": "c/uptodate", "version": "1.0.0" },
+        { "name": "d/removed", "version": "1.0.0" }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": {
+        "b/unstable": 15
+    },
+    "platform": [],
+    "platform-dev": []
+}
+--INSTALLED--
+[
+    { "name": "a/old", "version": "0.9.0" },
+    { "name": "b/unstable", "version": "1.1.0-alpha" },
+    { "name": "c/uptodate", "version": "2.0.0" }
+]
+--RUN--
+update b/unstable
+--EXPECT-LOCK--
+{
+    "packages": [
+        { "name": "a/old", "version": "1.0.0", "type": "library" },
+        { "name": "b/unstable", "version": "1.0.0", "type": "library" },
+        { "name": "c/uptodate", "version": "1.0.0", "type": "library" }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": [],
+    "platform": [],
+    "platform-dev": []
+}
+--EXPECT--
+Updating a/old (0.9.0) to a/old (1.0.0)
+Updating c/uptodate (2.0.0) to c/uptodate (1.0.0)
+Updating b/unstable (1.1.0-alpha) to b/unstable (1.0.0)
diff --git a/tests/Composer/Test/Fixtures/installer/partial-update-without-lock.test b/tests/Composer/Test/Fixtures/installer/partial-update-without-lock.test
new file mode 100644
index 000000000..146277d02
--- /dev/null
+++ b/tests/Composer/Test/Fixtures/installer/partial-update-without-lock.test
@@ -0,0 +1,49 @@
+--TEST--
+Partial update without lock file should update everything whitelisted, remove overly unstable packages
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                { "name": "a/old", "version": "1.0.0" },
+                { "name": "a/old", "version": "2.0.0" },
+                { "name": "b/unstable", "version": "1.0.0" },
+                { "name": "b/unstable", "version": "1.1.0-alpha" },
+                { "name": "c/uptodate", "version": "1.0.0" },
+                { "name": "d/removed", "version": "1.0.0" }
+            ]
+        }
+    ],
+    "require": {
+        "a/old": "*",
+        "b/unstable": "*",
+        "c/uptodate": "*"
+    }
+}
+--INSTALLED--
+[
+    { "name": "a/old", "version": "1.0.0" },
+    { "name": "b/unstable", "version": "1.1.0-alpha" },
+    { "name": "c/uptodate", "version": "1.0.0" },
+    { "name": "d/removed", "version": "1.0.0" }
+]
+--RUN--
+update b/unstable
+--EXPECT-LOCK--
+{
+    "packages": [
+        { "name": "a/old", "version": "1.0.0", "type": "library" },
+        { "name": "b/unstable", "version": "1.0.0", "type": "library" },
+        { "name": "c/uptodate", "version": "1.0.0", "type": "library" },
+        { "name": "d/removed", "version": "1.0.0", "type": "library" }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": [],
+    "platform": [],
+    "platform-dev": []
+}
+--EXPECT--
+Updating b/unstable (1.1.0-alpha) to b/unstable (1.0.0)
diff --git a/tests/Composer/Test/Fixtures/installer/update-downgrades-unstable-packages.test b/tests/Composer/Test/Fixtures/installer/update-downgrades-unstable-packages.test
new file mode 100644
index 000000000..1b6e55ef9
--- /dev/null
+++ b/tests/Composer/Test/Fixtures/installer/update-downgrades-unstable-packages.test
@@ -0,0 +1,49 @@
+--TEST--
+Downgrading from unstable to more stable package should work even if already installed
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                {
+                    "name": "a/a", "version": "dev-master",
+                    "source": { "reference": "abcd", "url": "", "type": "git" }
+                },
+                {
+                    "name": "a/a", "version": "1.0.0",
+                    "source": { "reference": "1.0.0", "url": "", "type": "git" },
+                    "dist": { "reference": "1.0.0", "url": "", "type": "zip", "shasum": "" }
+                },
+                {
+                    "name": "b/b", "version": "dev-master",
+                    "source": { "reference": "abcd", "url": "", "type": "git" }
+                },
+                {
+                    "name": "b/b", "version": "1.0.0",
+                    "source": { "reference": "1.0.0", "url": "", "type": "git" },
+                    "dist": { "reference": "1.0.0", "url": "", "type": "zip", "shasum": "" }
+                }
+            ]
+        }
+    ],
+    "require": {
+        "a/a": "*",
+        "b/b": "*@dev"
+    }
+}
+--INSTALLED--
+[
+    {
+        "name": "a/a", "version": "dev-master",
+        "source": { "reference": "abcd", "url": "", "type": "git" }
+    },
+    {
+        "name": "b/b", "version": "dev-master",
+        "source": { "reference": "abcd", "url": "", "type": "git" }
+    }
+]
+--RUN--
+update
+--EXPECT--
+Updating a/a (dev-master abcd) to a/a (1.0.0)
diff --git a/tests/Composer/Test/Mock/InstallationManagerMock.php b/tests/Composer/Test/Mock/InstallationManagerMock.php
index 0ecca1e2a..985b85879 100644
--- a/tests/Composer/Test/Mock/InstallationManagerMock.php
+++ b/tests/Composer/Test/Mock/InstallationManagerMock.php
@@ -33,6 +33,11 @@ class InstallationManagerMock extends InstallationManager
         return '';
     }
 
+    public function isPackageInstalled(InstalledRepositoryInterface $repo, PackageInterface $package)
+    {
+        return $repo->hasPackage($package);
+    }
+
     public function install(RepositoryInterface $repo, InstallOperation $operation)
     {
         $this->installed[] = $operation->getPackage();