diff --git a/package.json b/package.json
index c20996da39..ee4cea354b 100644
--- a/package.json
+++ b/package.json
@@ -37,7 +37,7 @@
     "test:all": "pnpm test:parallel && pnpm test:sequential",
     "test:parallel": "pnpm --filter=!server --filter=!ckeditor5-mermaid --filter=!ckeditor5-math --parallel test",
     "test:sequential": "pnpm --filter=server --filter=ckeditor5-mermaid --filter=ckeditor5-math --sequential test",
-    "typecheck": "tsc --build",
+    "typecheck": "tsc --build | tsx scripts/filter-tsc-output.mts",
     "dev:format-check": "eslint -c eslint.format.config.mjs .",
     "dev:format-fix": "eslint -c eslint.format.config.mjs . --fix",
     "dev:linter-check": "cross-env NODE_OPTIONS=--max_old_space_size=4096 eslint .",
diff --git a/scripts/filter-tsc-output.mts b/scripts/filter-tsc-output.mts
new file mode 100644
index 0000000000..754be10f66
--- /dev/null
+++ b/scripts/filter-tsc-output.mts
@@ -0,0 +1,24 @@
+/**
+ * Filters out TS6305 cascade errors from tsc --build output.
+ * These "Output file has not been built from source" errors are noise
+ * caused by upstream build failures and obscure the real errors.
+ */
+
+const SUPPRESSED_CODES = ["TS6305"];
+
+let data = "";
+process.stdin.resume();
+process.stdin.setEncoding("utf-8");
+process.stdin.on("data", (chunk) => (data += chunk));
+process.stdin.on("end", () => {
+    const filtered = data
+        .split(/\r?\n/)
+        .filter((line) => !SUPPRESSED_CODES.some((code) => line.includes(code)))
+        .join("\n")
+        .trim();
+
+    if (filtered) {
+        console.log(filtered);
+        process.exit(1);
+    }
+});