diff --git a/src/application/javascript/JavaScriptArtifactPathResolution.ts b/src/application/javascript/JavaScriptArtifactPathResolution.ts
index 90c79b20a0..b5ba5847be 100644
--- a/src/application/javascript/JavaScriptArtifactPathResolution.ts
+++ b/src/application/javascript/JavaScriptArtifactPathResolution.ts
@@ -496,12 +496,24 @@ const packageExport = (
   value: unknown,
   moduleKind: ResolveArtifactPathInput["moduleKind"],
 ): PackageExportOutcome => {
+  if (typeof value === "object" && value !== null && !Array.isArray(value)) {
+    const keys = Object.keys(value);
+    if (
+      keys.some((key) => key.startsWith(".")) &&
+      keys.some((key) => !key.startsWith("."))
+    )
+      return {
+        status: "rejected",
+        limitation:
+          "The package exports configuration mixes subpath keys and condition keys.",
+      };
+  }
   const root =
     typeof value === "object" && value !== null && Object.hasOwn(value, ".")
       ? Reflect.get(value, ".")
       : value;
   const flattened = exportTargets(root, packageExportConditions(moduleKind));
-  if (flattened.kind === "invalid")
+  if (flattened.kind === "invalid" || flattened.kind === "invalid-config")
     return { status: "rejected", limitation: flattened.limitation };
   const first =
     flattened.kind === "unmatched" ? undefined : flattened.values[0];
@@ -517,7 +529,8 @@ const packageExport = (
 type ExportTargets =
   | { readonly kind: "targets"; readonly values: readonly string[] }
   | { readonly kind: "unmatched" }
-  | { readonly kind: "invalid"; readonly limitation: string };
+  | { readonly kind: "invalid"; readonly limitation: string }
+  | { readonly kind: "invalid-config"; readonly limitation: string };
 
 const invalidExportTarget = (
   value: unknown,
@@ -570,6 +583,8 @@ const exportTargets = (
     let invalid: string | null = null;
     for (const entry of value) {
       const nested = exportTargets(entry, conditions);
+      // Node's array fallback catches invalid targets, not invalid configuration.
+      if (nested.kind === "invalid-config") return nested;
       if (nested.kind === "invalid") {
         invalid = nested.limitation;
         continue;
@@ -587,6 +602,14 @@ const exportTargets = (
       value,
       "must be a relative string, object, array, or null",
     );
+  for (const key of Object.keys(value)) {
+    const numeric = Number(key);
+    if (String(numeric) === key && numeric >= 0 && numeric < 0xffff_ffff)
+      return {
+        kind: "invalid-config",
+        limitation: `The package exports configuration contains numeric condition key ${JSON.stringify(key)}.`,
+      };
+  }
   for (const [condition, target] of Object.entries(value)) {
     if (!conditions.has(condition)) continue;
     const nested = exportTargets(target, conditions);
diff --git a/tests/boundary/javascript/packageConditionalExports.test.ts b/tests/boundary/javascript/packageConditionalExports.test.ts
index 7c65b6d49b..190fa0b4ef 100644
--- a/tests/boundary/javascript/packageConditionalExports.test.ts
+++ b/tests/boundary/javascript/packageConditionalExports.test.ts
@@ -122,6 +122,42 @@ const expectNodeAgreement = async (
   return outcome;
 };
 describe("ordered package exports conditions", () => {
+  it.each([
+    { ".": "./default.cjs", import: "./specific.cjs" },
+    { default: "./default.cjs", "./feature": "./specific.cjs" },
+    { "0": "./specific.cjs", default: "./default.cjs" },
+    { ".": { "1.5": "./specific.cjs", default: "./default.cjs" } },
+    { node: [{ "4294967294": null }, "./array.cjs"], default: "./default.cjs" },
+  ])(
+    "rejects invalid exports configuration %j without fallback",
+    async (exportsMap) => {
+      for (const moduleKind of ["import", "require"] as const) {
+        const { node, node_error, outcome } = await compareWithNode(
+          exportsMap,
+          moduleKind,
+        );
+        expect(node).toBeNull();
+        expect(node_error).toBe("ERR_INVALID_PACKAGE_CONFIG");
+        expect(outcome).toMatchObject({
+          resolved_path: null,
+          resolution_status: "rejected",
+        });
+        expect(outcome.limitations[0]).toContain("exports configuration");
+      }
+    },
+  );
+
+  it.each([
+    { "01": "./specific.cjs", default: "./default.cjs" },
+    { "4294967295": "./specific.cjs", default: "./default.cjs" },
+    { browser: { "0": null }, default: "./default.cjs" },
+    ["./default.cjs", { "0": null }],
+    { ".": "./default.cjs", "./feature": "./specific.cjs" },
+  ])("preserves valid or unvisited conditions in %j", async (exportsMap) => {
+    for (const moduleKind of ["import", "require"] as const)
+      await expectNodeAgreement(exportsMap, "default.cjs", moduleKind);
+  });
+
   it.each(["import", "require"] as const)(
     "matches Node when default precedes %s",
     async (moduleKind) => {