diff --git a/packages/clerk-js/src/core/__tests__/clerk.test.ts b/packages/clerk-js/src/core/__tests__/clerk.test.ts
index 1cccffbbcd8..e7eae3e57e9 100644
--- a/packages/clerk-js/src/core/__tests__/clerk.test.ts
+++ b/packages/clerk-js/src/core/__tests__/clerk.test.ts
@@ -378,6 +378,33 @@ describe('Clerk singleton', () => {
         });
       });
 
+      it('throws an error when setting active organization with invalid slug', async () => {
+        const mockSession2 = {
+          id: '1',
+          status,
+          user: {
+            organizationMemberships: [
+              {
+                id: 'orgmem_id',
+                organization: {
+                  id: 'org_id',
+                  slug: 'valid-org-slug',
+                },
+              },
+            ],
+          },
+          touch: vi.fn(),
+          getToken: vi.fn(),
+        };
+        mockClientFetch.mockReturnValue(Promise.resolve({ signedInSessions: [mockSession2] }));
+        const sut = new Clerk(productionPublishableKey);
+        await sut.load();
+
+        await expect(sut.setActive({ organization: 'invalid-org-slug' })).rejects.toThrow(
+          'Unable to find organization with slug "invalid-org-slug". The user is not a member of this organization or it does not exist.',
+        );
+      });
+
       it('redirects the user to the /v1/client/touch endpoint if the cookie_expires_at is less than 8 days away', async () => {
         mockSession.touch.mockReturnValue(Promise.resolve());
         mockClientFetch.mockReturnValue(
diff --git a/packages/clerk-js/src/core/clerk.ts b/packages/clerk-js/src/core/clerk.ts
index 1d9f44f5258..eb21c501261 100644
--- a/packages/clerk-js/src/core/clerk.ts
+++ b/packages/clerk-js/src/core/clerk.ts
@@ -1351,6 +1351,16 @@ export class Clerk implements ClerkInterface {
           const newLastActiveOrganizationId = matchingOrganization?.organization.id || null;
           const isPersonalWorkspace = newLastActiveOrganizationId === null;
 
+        const INVALID_ORGANIZATION_SLUG_ERROR_CODE = 'invalid_organization_slug';
+
+        // If a slug was explicitly provided but doesn't match any organization, throw an error
+        if (organizationIdOrSlug && !matchingOrganization) {
+          throw new ClerkRuntimeError(
+            `Unable to find organization with slug "${organizationIdOrSlug}". The user is not a member of this organization or it does not exist.`,
+            { code: INVALID_ORGANIZATION_SLUG_ERROR_CODE }
+          );
+        }
+
           // Do not update in-memory to personal workspace if force organization selection is enabled
           if (this.environment?.organizationSettings?.forceOrganizationSelection && isPersonalWorkspace) {
             return;