diff --git a/src/many-web/src/error.rs b/src/many-web/src/error.rs
index bd9af763..f1013fbe 100644
--- a/src/many-web/src/error.rs
+++ b/src/many-web/src/error.rs
@@ -22,6 +22,7 @@ define_attribute_many_error!(
         17: pub fn site_name_too_long(site_name) => "Site name too long: {site_name}.",
         18: pub fn invalid_domain(domain) => "Invalid domain: {domain}.",
         19: pub fn page_size_too_large(size) => "Page size too large: {size}.",
+        20: pub fn domain_already_in_use(domain) => "Domain already in use: {domain}.",
     }
 );
 
diff --git a/src/many-web/src/module.rs b/src/many-web/src/module.rs
index 039f80e1..132a8c9d 100644
--- a/src/many-web/src/module.rs
+++ b/src/many-web/src/module.rs
@@ -274,6 +274,12 @@ impl WebCommandsModuleBackend for WebModuleImpl {
             return Err(error::existent_site(site_name));
         }
 
+        if let Some(domain) = &domain {
+            if self.storage.has_domain(domain) {
+                return Err(error::domain_already_in_use(domain));
+            }
+        }
+
         let tmpdir = Builder::new()
             .prefix("dweb-")
             .tempdir()
@@ -368,6 +374,12 @@ impl WebCommandsModuleBackend for WebModuleImpl {
             return Err(error::nonexistent_site(site_name));
         }
 
+        if let Some(domain) = &domain {
+            if self.storage.has_domain(domain) {
+                return Err(error::domain_already_in_use(domain));
+            }
+        }
+
         let tmpdir = Builder::new()
             .prefix("dweb-")
             .tempdir()
diff --git a/src/many-web/src/storage.rs b/src/many-web/src/storage.rs
index 5b8e2c68..4f4907d0 100644
--- a/src/many-web/src/storage.rs
+++ b/src/many-web/src/storage.rs
@@ -460,6 +460,12 @@ impl WebStorage {
             .map_err(error::storage_get_failed)
     }
 
+    // Check all websites for a given domain
+    pub fn has_domain(&self, domain: &String) -> bool {
+        self.list(SortOrder::Descending, None)
+            .any(|(_, meta)| meta.domain.as_ref() == Some(domain))
+    }
+
     pub fn list(
         &self,
         order: SortOrder,
diff --git a/tests/e2e/web/web.bats b/tests/e2e/web/web.bats
index dc07f030..a8007517 100644
--- a/tests/e2e/web/web.bats
+++ b/tests/e2e/web/web.bats
@@ -60,6 +60,29 @@ function teardown() {
     assert_output --partial "Nonexistent site: test_dweb"
 }
 
+@test "$SUITE dweb deploy fails if domain already in use" {
+    call_web --pem=1 --port=8000 deploy test_dweb test_dweb.zip --domain foobar.com
+    assert_output --partial "https://test_dweb-$(identity 1).ghostcloud.org"
+    assert_output --partial "foobar.com"
+
+    # We check all websites, not just the ones owned by the sender
+    call_web --pem=2 --port=8000 deploy test_dweb2 test_dweb.zip --domain foobar.com
+    assert_output --partial "Domain already in use: foobar.com."
+}
+
+@test "$SUITE dweb update fails if domain already in use" {
+    call_web --pem=1 --port=8000 deploy test_dweb test_dweb.zip --domain foobar.com
+    assert_output --partial "https://test_dweb-$(identity 1).ghostcloud.org"
+    assert_output --partial "foobar.com"
+
+    call_web --pem=1 --port=8000 deploy test_dweb2 test_dweb.zip
+    assert_output --partial "https://test_dweb2-$(identity 1).ghostcloud.org"
+    refute_output --partial "foobar.com"
+
+    call_web --pem=1 --port=8000 update test_dweb2 test_dweb.zip --domain foobar.com
+    assert_output --partial "Domain already in use: foobar.com."
+}
+
 @test "$SUITE: dweb website removal works" {
     call_web --pem=1 --port=8000 deploy test_dweb test_dweb.zip
     assert_output  --partial "https://test_dweb-$(identity 1).ghostcloud.org"