diff --git a/src/Composer/DependencyResolver/PoolOptimizer.php b/src/Composer/DependencyResolver/PoolOptimizer.php
index bfb10a589269..4aa6ffe324d8 100644
--- a/src/Composer/DependencyResolver/PoolOptimizer.php
+++ b/src/Composer/DependencyResolver/PoolOptimizer.php
@@ -418,6 +418,19 @@ private function optimizeImpossiblePackagesAway(Request $request, Pool $pool)
         }
 
         foreach ($request->getLockedPackages() as $package) {
+            // If this locked package is no longer required by root or anything in the pool, it may get uninstalled so do not apply its requirements
+            // In a case where a requirement WERE to appear in the pool by a package that would not be used, it would've been unlocked and so not filtered still
+            $ignoreUnusedPackage = false;
+            foreach ($package->getNames(false) as $packageName) {
+                if (!isset($this->requireConstraintsPerPackage[$packageName])) {
+                    $ignoreUnusedPackage = true;
+                }
+            }
+
+            if ($ignoreUnusedPackage) {
+                continue;
+            }
+
             foreach ($package->getRequires() as $link) {
                 $require = $link->getTarget();
                 if (!isset($packageIndex[$require])) {
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/filter-impossible-oackages-only-required.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/filter-impossible-oackages-only-required.test
new file mode 100644
index 000000000000..2705f2d4e088
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/filter-impossible-oackages-only-required.test
@@ -0,0 +1,54 @@
+--TEST--
+When filtering packages from the pool that cannot meet the fixed/locked requirements, ensure that the requirements for a package that is not required anywhere is not used to filter, as it will be ultimately be removed.
+
+--REQUEST--
+{
+    "require": {
+        "first/pkg": "*",
+        "second/pkg": "1.1.0"
+    },
+    "locked": [
+        {"name": "first/pkg", "version": "1.0.0", "require": {"second/pkg": "^1.0"}},
+        {"name": "second/pkg", "version": "1.0.0", "require": {"third/pkg": "1.0.0"}},
+        {"name": "third/pkg", "version": "1.0.0", "require": {"fourth/pkg": "1.0.0"}},
+        {"name": "fourth/pkg", "version": "1.0.0"}
+    ],
+    "allowList": [
+        "first/pkg"
+    ],
+    "allowTransitiveDeps": true
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "first/pkg", "version": "1.0.0", "require": {"second/pkg": "*"}},
+        {"name": "second/pkg", "version": "1.0.0", "require": {"third/pkg": "1.0.0"}},
+        {"name": "second/pkg", "version": "1.1.0", "require": {"fourth/pkg": "2.0.0"}},
+        {"name": "third/pkg", "version": "1.0.0", "require": {"fourth/pkg": "1.0.0"}},
+        {"name": "fourth/pkg", "version": "1.0.0"},
+        {"name": "fourth/pkg", "version": "2.0.0"}
+    ]
+]
+
+--EXPECT--
+[
+    "third/pkg-1.0.0.0 (locked)",
+    "first/pkg-1.0.0.0",
+    "second/pkg-1.1.0.0",
+    "fourth/pkg-1.0.0.0",
+    "fourth/pkg-2.0.0.0"
+]
+
+--EXPECT-OPTIMIZED--
+[
+    "third/pkg-1.0.0.0 (locked)",
+    "first/pkg-1.0.0.0",
+    "second/pkg-1.1.0.0",
+    "fourth/pkg-1.0.0.0",
+    "fourth/pkg-2.0.0.0"
+]