diff --git a/packages/mcp-core/src/tools/support/issue-linking/app.test.ts b/packages/mcp-core/src/tools/support/issue-linking/app.test.ts
index 6276e6d62..98760200c 100644
--- a/packages/mcp-core/src/tools/support/issue-linking/app.test.ts
+++ b/packages/mcp-core/src/tools/support/issue-linking/app.test.ts
@@ -287,6 +287,13 @@ describe("linkAppIssue", () => {
     expect(searches).toBe(1);
   });
 
+  it("says the App must be installed when the organization has no installation", async () => {
+    mockDiscovery({ slug: "other" });
+    await expect(linkAppIssue(api, params)).rejects.toThrow(
+      "The 'linear' Sentry App is not installed in organization 'example'",
+    );
+  });
+
   it("requires a valid installed callback even for an existing association", async () => {
     mockDiscovery({
       links: [association],
diff --git a/packages/mcp-core/src/tools/support/issue-linking/app.ts b/packages/mcp-core/src/tools/support/issue-linking/app.ts
index ce193039c..e17c566f6 100644
--- a/packages/mcp-core/src/tools/support/issue-linking/app.ts
+++ b/packages/mcp-core/src/tools/support/issue-linking/app.ts
@@ -317,7 +317,11 @@ export async function linkAppIssue(
     (installation) =>
       installation.app.slug === appSlug && installation.status === "installed",
   );
-  if (installed.length !== 1)
+  if (installed.length === 0)
+    throw new UserInputError(
+      `The '${appSlug}' Sentry App is not installed in organization '${params.organizationSlug}', so Sentry cannot link this issue to it. Someone who can manage integrations must install it under Settings > Integrations in Sentry, then retry.`,
+    );
+  if (installed.length > 1)
     throw new UserInputError(`Expected one installed Sentry App '${appSlug}'.`);
   const installation = installed[0]!;
   const matchingComponents = components.filter(