Remove default branch alias from versions which are numeric, fixes #9705

src/Composer/Package/Loader/ArrayLoader.php

@@ -375,7 +375,12 @@ class ArrayLoader implements LoaderInterface
             }
         }
 
-        if (isset($config['default-branch']) && $config['default-branch'] === true) {
+
+        if (
+            isset($config['default-branch'])
+            && $config['default-branch'] === true
+            && false === $this->versionParser->parseNumericAliasPrefix($config['version'])
+        ) {
             return VersionParser::DEFAULT_BRANCH_ALIAS;
         }
     }

tests/Composer/Test/Fixtures/installer/unbounded-conflict-does-not-match-default-branch-with-numeric-branch.test

@@ -0,0 +1,30 @@
+--TEST--
+Test that a conflict against >=5 does not include the default branch if it is a numeric branch.
+--COMPOSER--
+{
+    "repositories": [
+        {
+            "type": "package",
+            "package": [
+                { "name": "conflicter/pkg", "version": "1.0.0", "conflict": { "victim/pkg": ">=5", "victim/pkg2": ">=5" } },
+                { "name": "victim/pkg", "version": "3.x-dev", "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--
+Installing conflicter/pkg (1.0.0)
+Installing victim/pkg (3.x-dev)
+Installing victim/pkg2 (dev-foo)