diff --git a/packages/junior/src/chat/tools/sandbox/grep.ts b/packages/junior/src/chat/tools/sandbox/grep.ts
index 1f32223249..0773708c94 100644
--- a/packages/junior/src/chat/tools/sandbox/grep.ts
+++ b/packages/junior/src/chat/tools/sandbox/grep.ts
@@ -334,7 +334,7 @@ async function grepFilesWithRipgrep(params: {
         cause: new Error(detail),
       });
     }
-    if (/regex parse error|error parsing regex/i.test(detail)) {
+    if (/regex parse error|error parsing regex|is not allowed in a regex/i.test(detail)) {
       throw new ToolInputError(`Invalid regex pattern: ${params.pattern}`, {
         cause: new Error(detail),
       });
diff --git a/packages/junior/tests/unit/tools/sandbox/file-tools.test.ts b/packages/junior/tests/unit/tools/sandbox/file-tools.test.ts
index cf65c1f4e5..988662413e 100644
--- a/packages/junior/tests/unit/tools/sandbox/file-tools.test.ts
+++ b/packages/junior/tests/unit/tools/sandbox/file-tools.test.ts
@@ -416,6 +416,24 @@ describe("sandbox file tools", () => {
       message: "Invalid glob: {foo,{bar,baz}}",
     });
 
+    const literalNewline: SandboxCommandRunner = async () => ({
+      exitCode: 2,
+      stderr: 'rg: the literal "\\n" is not allowed in a regex',
+      stdout: "",
+    });
+
+    await expect(
+      grepFiles({
+        fs: memory.fs,
+        path: "src",
+        pattern: "foo\nbar",
+        runCommand: literalNewline,
+      }),
+    ).rejects.toMatchObject({
+      name: "ToolInputError",
+      message: "Invalid regex pattern: foo\nbar",
+    });
+
     const lifecycleFailure = new Error("sandbox_stopped");
     await expect(
       findFiles({