diff --git a/src/Composer/DependencyResolver/Decisions.php b/src/Composer/DependencyResolver/Decisions.php
index 2fdf6da74..02997819e 100644
--- a/src/Composer/DependencyResolver/Decisions.php
+++ b/src/Composer/DependencyResolver/Decisions.php
@@ -197,16 +197,21 @@ class Decisions implements \Iterator, \Countable
         }
     }
 
-    public function __toString()
+    public function toString(Pool $pool = null)
     {
         $decisionMap = $this->decisionMap;
         ksort($decisionMap);
         $str = '[';
         foreach ($decisionMap as $packageId => $level) {
-            $str .= $packageId.':'.$level.',';
+            $str .= (($pool) ? $pool->literalToPackage($packageId) : $packageId).':'.$level.',';
         }
         $str .= ']';
 
         return $str;
     }
+
+    public function __toString()
+    {
+        return $this->toString();
+    }
 }
diff --git a/src/Composer/DependencyResolver/Rule.php b/src/Composer/DependencyResolver/Rule.php
index eb0f6e296..5571ec676 100644
--- a/src/Composer/DependencyResolver/Rule.php
+++ b/src/Composer/DependencyResolver/Rule.php
@@ -34,7 +34,7 @@ abstract class Rule
     const RULE_PACKAGE_SAME_NAME = 10;
     const RULE_LEARNED = 12;
     const RULE_PACKAGE_ALIAS = 13;
-    const RULE_PACKAGE_ROOT_ALIAS = 14;
+    const RULE_PACKAGE_INVERSE_ALIAS = 14;
 
     // bitfield defs
     const BITFIELD_TYPE = 0;
@@ -311,22 +311,26 @@ abstract class Rule
 
                 return 'Conclusion: '.$ruleText.$learnedString;
             case self::RULE_PACKAGE_ALIAS:
-            case self::RULE_PACKAGE_ROOT_ALIAS:
-                if ($this->getReason() === self::RULE_PACKAGE_ALIAS) {
-                    $aliasPackage = $pool->literalToPackage($literals[0]);
-                    $otherLiteral = 1;
-                } else {
-                    // root alias rules work the other way around
-                    $aliasPackage = $pool->literalToPackage($literals[1]);
-                    $otherLiteral = 0;
-                }
+                $aliasPackage = $pool->literalToPackage($literals[0]);
+
                 // avoid returning content like "9999999-dev is an alias of dev-master" as it is useless
                 if ($aliasPackage->getVersion() === VersionParser::DEFAULT_BRANCH_ALIAS) {
                     return '';
                 }
-                $package = $this->deduplicateDefaultBranchAlias($pool->literalToPackage($literals[$otherLiteral]));
+                $package = $this->deduplicateDefaultBranchAlias($pool->literalToPackage($literals[1]));
 
                 return $aliasPackage->getPrettyString() .' is an alias of '.$package->getPrettyString().' and thus requires it to be installed too.';
+            case self::RULE_PACKAGE_INVERSE_ALIAS:
+                // inverse alias rules work the other way around than above
+                $aliasPackage = $pool->literalToPackage($literals[1]);
+
+                // avoid returning content like "9999999-dev is an alias of dev-master" as it is useless
+                if ($aliasPackage->getVersion() === VersionParser::DEFAULT_BRANCH_ALIAS) {
+                    return '';
+                }
+                $package = $this->deduplicateDefaultBranchAlias($pool->literalToPackage($literals[0]));
+
+                return $aliasPackage->getPrettyString() .' is an alias of '.$package->getPrettyString().' and must be installed with it.';
             default:
                 $ruleText = '';
                 foreach ($literals as $i => $literal) {
diff --git a/src/Composer/DependencyResolver/RuleSetGenerator.php b/src/Composer/DependencyResolver/RuleSetGenerator.php
index edd492b4e..ec8f9ed8c 100644
--- a/src/Composer/DependencyResolver/RuleSetGenerator.php
+++ b/src/Composer/DependencyResolver/RuleSetGenerator.php
@@ -164,10 +164,8 @@ class RuleSetGenerator
                 $workQueue->enqueue($package->getAliasOf());
                 $this->addRule(RuleSet::TYPE_PACKAGE, $this->createRequireRule($package, array($package->getAliasOf()), Rule::RULE_PACKAGE_ALIAS, $package));
 
-                // root aliases must be installed with their main package, so create a rule the other way around as well
-                if ($package->isRootPackageAlias()) {
-                    $this->addRule(RuleSet::TYPE_PACKAGE, $this->createRequireRule($package->getAliasOf(), array($package), Rule::RULE_PACKAGE_ROOT_ALIAS, $package->getAliasOf()));
-                }
+                // aliases must be installed with their main package, so create a rule the other way around as well
+                $this->addRule(RuleSet::TYPE_PACKAGE, $this->createRequireRule($package->getAliasOf(), array($package), Rule::RULE_PACKAGE_INVERSE_ALIAS, $package->getAliasOf()));
 
                 // if alias package has no self.version requires, its requirements do not
                 // need to be added as the aliased package processing will take care of it
@@ -197,6 +195,7 @@ class RuleSetGenerator
         /** @var PackageInterface $package */
         foreach ($this->addedMap as $package) {
             foreach ($package->getConflicts() as $link) {
+                // even if conlict ends up being with an alias, there would be at least one actual package by this name
                 if (!isset($this->addedPackagesByNames[$link->getTarget()])) {
                     continue;
                 }
@@ -205,10 +204,14 @@ class RuleSetGenerator
                     continue;
                 }
 
-                /** @var PackageInterface $possibleConflict */
-                foreach ($this->addedPackagesByNames[$link->getTarget()] as $possibleConflict) {
-                    if ($this->pool->match($possibleConflict, $link->getTarget(), $link->getConstraint())) {
-                        $this->addRule(RuleSet::TYPE_PACKAGE, $this->createRule2Literals($package, $possibleConflict, Rule::RULE_PACKAGE_CONFLICT, $link));
+                $conflicts = $this->pool->whatProvides($link->getTarget(), $link->getConstraint());
+
+                foreach ($conflicts as $conflict) {
+                    // define the conflict rule for regular packages, for alias packages it's only needed if the name
+                    // matches the conflict exactly, otherwise the name match is by provide/replace which means the
+                    // package which this is an alias of will conflict anyway, so no need to create additional rules
+                    if (!$conflict instanceof AliasPackage || $conflict->getName() === $link->getTarget()) {
+                        $this->addRule(RuleSet::TYPE_PACKAGE, $this->createRule2Literals($package, $conflict, Rule::RULE_PACKAGE_CONFLICT, $link));
                     }
                 }
             }
@@ -266,9 +269,13 @@ class RuleSetGenerator
     protected function addRulesForRootAliases($ignorePlatformReqs)
     {
         foreach ($this->pool->getPackages() as $package) {
-            // ensure that rules for root alias packages get loaded even if the root alias itself isn't required
-            // otherwise a package could be installed without its root alias which leads to unexpected behavior
-            if ($package instanceof AliasPackage && $package->isRootPackageAlias()) {
+            // ensure that rules for root alias packages and aliases of packages which were loaded are also loaded
+            // even if the alias itself isn't required, otherwise a package could be installed without its alias which
+            // leads to unexpected behavior
+            if (!isset($this->addedMap[$package->id]) &&
+                $package instanceof AliasPackage &&
+                ($package->isRootPackageAlias() || isset($this->addedMap[$package->getAliasOf()->id]))
+            ) {
                 $this->addRulesForPackage($package, $ignorePlatformReqs);
             }
         }
diff --git a/tests/Composer/Test/DependencyResolver/SolverTest.php b/tests/Composer/Test/DependencyResolver/SolverTest.php
index 25992e58b..cf916fb6b 100644
--- a/tests/Composer/Test/DependencyResolver/SolverTest.php
+++ b/tests/Composer/Test/DependencyResolver/SolverTest.php
@@ -840,6 +840,7 @@ class SolverTest extends TestCase
             array('job' => 'install', 'package' => $packageB),
             array('job' => 'markAliasInstalled', 'package' => $packageBAlias),
             array('job' => 'install', 'package' => $packageC),
+            array('job' => 'markAliasInstalled', 'package' => $packageCAlias),
         ));
     }
 
diff --git a/tests/Composer/Test/Fixtures/installer/conflict-on-root-with-alias-prevents-update-if-not-required.test b/tests/Composer/Test/Fixtures/installer/conflict-on-root-with-alias-prevents-update-if-not-required.test
new file mode 100644
index 000000000..3a457b22c
--- /dev/null
+++ b/tests/Composer/Test/Fixtures/installer/conflict-on-root-with-alias-prevents-update-if-not-required.test
@@ -0,0 +1,38 @@
+--TEST--
+Test that a root package conflict with a branch alias leads to an error, even if the branch alias isn't required.
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                { "name": "some/dep", "version": "1.0.0" },
+                { "name": "some/dep", "version": "1.1.0" },
+                { "name": "some/dep", "version": "1.2.0" },
+                { "name": "some/dep", "version": "dev-main", "extra": {"branch-alias": {"dev-main": "1.3.x-dev"} } },
+                { "name": "some/dep", "version": "1.2.x-dev" }
+            ]
+        }
+    ],
+    "require": {
+        "some/dep": "dev-main"
+    },
+    "conflict": {
+        "some/dep": ">=1.3"
+    }
+}
+--RUN--
+update
+--EXPECT-EXIT-CODE--
+2
+--EXPECT-OUTPUT--
+Loading composer repositories with package information
+Updating dependencies
+Your requirements could not be resolved to an installable set of packages.
+
+  Problem 1
+    - __root__ is present at version 1.0.0+no-version-set and cannot be modified by Composer
+    - some/dep 1.3.x-dev is an alias of some/dep dev-main and must be installed with it.
+    - __root__ 1.0.0+no-version-set conflicts with some/dep 1.3.x-dev.
+    - Root composer.json requires some/dep dev-main -> satisfiable by some/dep[dev-main].
+--EXPECT--
diff --git a/tests/Composer/Test/Fixtures/installer/conflict-with-alias-in-lock-does-prevents-install.test b/tests/Composer/Test/Fixtures/installer/conflict-with-alias-in-lock-does-prevents-install.test
new file mode 100644
index 000000000..c19ca396c
--- /dev/null
+++ b/tests/Composer/Test/Fixtures/installer/conflict-with-alias-in-lock-does-prevents-install.test
@@ -0,0 +1,54 @@
+--TEST--
+Test that conflict with a branch alias in the lock file leads to an error on install from lock, even if the branch alias was removed on the remote end.
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                { "name": "some/dep", "version": "1.0.0" },
+                { "name": "some/dep", "version": "1.1.0" },
+                { "name": "some/dep", "version": "1.2.0" },
+                { "name": "some/dep", "version": "dev-main" },
+                { "name": "some/dep", "version": "1.2.x-dev" },
+                { "name": "conflictor/foo", "version": "1.0.0", "conflict": { "some/dep": ">=1.3" } }
+            ]
+        }
+    ],
+    "require": {
+        "some/dep": "dev-main",
+        "conflictor/foo": "1.0.0"
+    }
+}
+--LOCK--
+{
+    "packages": [
+        { "name": "conflictor/foo", "version": "1.0.0", "conflict": { "some/dep": ">=1.3" }, "type": "library" },
+        { "name": "some/dep", "version": "dev-main", "extra": {"branch-alias": {"dev-main": "1.3.x-dev"} }, "type": "library" }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": {
+        "some/dep": 20
+    },
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": [],
+    "platform-dev": []
+}
+--RUN--
+install
+--EXPECT-EXIT-CODE--
+2
+--EXPECT-OUTPUT--
+Installing dependencies from lock file (including require-dev)
+Verifying lock file contents can be installed on current platform.
+Your lock file does not contain a compatible set of packages. Please run composer update.
+
+  Problem 1
+    - conflictor/foo is locked to version 1.0.0 and an update of this package was not requested.
+    - conflictor/foo 1.0.0 conflicts with some/dep 1.3.x-dev.
+    - some/dep is locked to version 1.3.x-dev and an update of this package was not requested.
+
+--EXPECT--
diff --git a/tests/Composer/Test/Fixtures/installer/conflict-with-alias-prevents-update-if-not-required.test b/tests/Composer/Test/Fixtures/installer/conflict-with-alias-prevents-update-if-not-required.test
new file mode 100644
index 000000000..78cfd0362
--- /dev/null
+++ b/tests/Composer/Test/Fixtures/installer/conflict-with-alias-prevents-update-if-not-required.test
@@ -0,0 +1,38 @@
+--TEST--
+Test that conflict of a dependency with a branch alias of another dependency is not ignored, even if the alias is not required for installation.
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                { "name": "some/dep", "version": "1.0.0" },
+                { "name": "some/dep", "version": "1.1.0" },
+                { "name": "some/dep", "version": "1.2.0" },
+                { "name": "some/dep", "version": "dev-main", "extra": {"branch-alias": {"dev-main": "1.3.x-dev"} } },
+                { "name": "some/dep", "version": "1.2.x-dev" },
+                { "name": "conflictor/foo", "version": "1.0.0", "conflict": { "some/dep": ">=1.3" } }
+            ]
+        }
+    ],
+    "require": {
+        "some/dep": "dev-main",
+        "conflictor/foo": "1.0.0"
+    }
+}
+--RUN--
+update
+--EXPECT-EXIT-CODE--
+2
+--EXPECT-OUTPUT--
+Loading composer repositories with package information
+Updating dependencies
+Your requirements could not be resolved to an installable set of packages.
+
+  Problem 1
+    - Root composer.json requires some/dep dev-main -> satisfiable by some/dep[dev-main].
+    - conflictor/foo 1.0.0 conflicts with some/dep 1.3.x-dev.
+    - some/dep 1.3.x-dev is an alias of some/dep dev-main and must be installed with it.
+    - Root composer.json requires conflictor/foo 1.0.0 -> satisfiable by conflictor/foo[1.0.0].
+
+--EXPECT--
diff --git a/tests/Composer/Test/Fixtures/installer/conflict-with-alias-prevents-update.test b/tests/Composer/Test/Fixtures/installer/conflict-with-alias-prevents-update.test
new file mode 100644
index 000000000..74b61304e
--- /dev/null
+++ b/tests/Composer/Test/Fixtures/installer/conflict-with-alias-prevents-update.test
@@ -0,0 +1,43 @@
+--TEST--
+Test that conflict on a branch alias is respected
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                { "name": "some/dep", "version": "1.0.0" },
+                { "name": "some/dep", "version": "1.1.0" },
+                { "name": "some/dep", "version": "1.2.0" },
+                { "name": "some/dep", "version": "dev-main", "extra": {"branch-alias": {"dev-main": "1.3.x-dev"} } },
+                { "name": "some/dep", "version": "1.2.x-dev" }
+            ]
+        }
+    ],
+    "require": {
+        "some/dep": "^1.0@dev"
+    },
+    "conflict": {
+        "some/dep": ">=1.3"
+    }
+}
+--RUN--
+update
+--EXPECT-LOCK--
+{
+    "packages": [
+        { "name": "some/dep", "version": "1.2.x-dev", "type": "library" }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": {
+        "some/dep": 20
+    },
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": [],
+    "platform-dev": []
+}
+--EXPECT--
+Installing some/dep (1.2.x-dev)
diff --git a/tests/Composer/Test/Fixtures/installer/unbounded-conflict-does-not-match-dev-master.test b/tests/Composer/Test/Fixtures/installer/unbounded-conflict-does-not-match-default-branch-with-branch-alias.test
similarity index 71%
rename from tests/Composer/Test/Fixtures/installer/unbounded-conflict-does-not-match-dev-master.test
rename to tests/Composer/Test/Fixtures/installer/unbounded-conflict-does-not-match-default-branch-with-branch-alias.test
index 900028457..ca891bbc1 100644
--- a/tests/Composer/Test/Fixtures/installer/unbounded-conflict-does-not-match-dev-master.test
+++ b/tests/Composer/Test/Fixtures/installer/unbounded-conflict-does-not-match-default-branch-with-branch-alias.test
@@ -1,5 +1,5 @@
 --TEST--
-Test that a conflict against >=5 does not include dev-master or other dev-x
+Test that a conflict against >=5 does not include the default branch if it has a branch alias defined.
 --COMPOSER--
 {
     "repositories": [
@@ -7,7 +7,7 @@ Test that a conflict against >=5 does not include dev-master or other dev-x
             "type": "package",
             "package": [
                 { "name": "conflicter/pkg", "version": "1.0.0", "conflict": { "victim/pkg": ">=5", "victim/pkg2": ">=5" } },
-                { "name": "victim/pkg", "version": "dev-master", "default-branch": true },
+                { "name": "victim/pkg", "version": "dev-master", "default-branch": true, "extra": { "branch-alias": { "dev-master": "2.x-dev" } } },
                 { "name": "victim/pkg2", "version": "dev-foo" }
             ]
         }
@@ -27,5 +27,5 @@ update
 --EXPECT--
 Installing conflicter/pkg (1.0.0)
 Installing victim/pkg (dev-master)
-Marking victim/pkg (9999999-dev) as installed, alias of victim/pkg (dev-master)
+Marking victim/pkg (2.x-dev) as installed, alias of victim/pkg (dev-master)
 Installing victim/pkg2 (dev-foo)
diff --git a/tests/Composer/Test/Fixtures/installer/unbounded-conflict-matches-default-branch.test b/tests/Composer/Test/Fixtures/installer/unbounded-conflict-matches-default-branch.test
new file mode 100644
index 000000000..d4a3b4d85
--- /dev/null
+++ b/tests/Composer/Test/Fixtures/installer/unbounded-conflict-matches-default-branch.test
@@ -0,0 +1,39 @@
+--TEST--
+Test that a conflict against >=5 includes the default branch if it has no branch alias defined (and then uses the default 9999999-dev alias).
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                { "name": "conflicter/pkg", "version": "1.0.0", "conflict": { "victim/pkg": ">=5", "victim/pkg2": ">=5" } },
+                { "name": "victim/pkg", "version": "dev-master", "default-branch": true },
+                { "name": "victim/pkg2", "version": "dev-foo" }
+            ]
+        }
+    ],
+    "require": {
+        "conflicter/pkg": "1.0.0",
+        "victim/pkg": "*",
+        "victim/pkg2": "*"
+    },
+    "minimum-stability": "dev"
+}
+
+
+--RUN--
+update
+
+--EXPECT-EXIT-CODE--
+2
+--EXPECT-OUTPUT--
+Loading composer repositories with package information
+Updating dependencies
+Your requirements could not be resolved to an installable set of packages.
+
+  Problem 1
+    - conflicter/pkg 1.0.0 conflicts with victim/pkg dev-master.
+    - Root composer.json requires conflicter/pkg 1.0.0 -> satisfiable by conflicter/pkg[1.0.0].
+    - Root composer.json requires victim/pkg * -> satisfiable by victim/pkg[dev-master].
+
+--EXPECT--