diff --git a/crates/crates-io/lib.rs b/crates/crates-io/lib.rs
index becd02af8..bd85e8697 100644
--- a/crates/crates-io/lib.rs
+++ b/crates/crates-io/lib.rs
@@ -149,15 +149,41 @@ impl Registry {
     pub fn add_owners(&mut self, krate: &str, owners: &[&str]) -> Result<String> {
         let body = serde_json::to_string(&OwnersReq { users: owners })?;
         let body = self.put(&format!("/crates/{}/owners", krate), body.as_bytes())?;
-        assert!(serde_json::from_str::<OwnerResponse>(&body)?.ok);
-        Ok(serde_json::from_str::<OwnerResponse>(&body)?.msg)
+        let body = if body.is_empty() {
+            r#"{"ok":false,"msg":"response body is empty"}"#.parse()?
+        } else {
+            body
+        };
+        match serde_json::from_str::<OwnerResponse>(&body) {
+            Ok(response) => {
+                if response.ok {
+                    Ok(response.msg)
+                } else {
+                    bail!("{}", response.msg)
+                }
+            }
+            _ => bail!("failed to parse response body"),
+        }
     }
 
-    pub fn remove_owners(&mut self, krate: &str, owners: &[&str]) -> Result<()> {
+    pub fn remove_owners(&mut self, krate: &str, owners: &[&str]) -> Result<String> {
         let body = serde_json::to_string(&OwnersReq { users: owners })?;
         let body = self.delete(&format!("/crates/{}/owners", krate), Some(body.as_bytes()))?;
-        assert!(serde_json::from_str::<OwnerResponse>(&body)?.ok);
-        Ok(())
+        let body = if body.is_empty() {
+            r#"{"ok":false,"msg":"response body is empty"}"#.parse()?
+        } else {
+            body
+        };
+        match serde_json::from_str::<OwnerResponse>(&body) {
+            Ok(response) => {
+                if response.ok {
+                    Ok(response.msg)
+                } else {
+                    bail!("{}", response.msg)
+                }
+            }
+            _ => bail!("failed to parse response body"),
+        }
     }
 
     pub fn list_owners(&mut self, krate: &str) -> Result<Vec<User>> {
diff --git a/src/doc/src/reference/registries.md b/src/doc/src/reference/registries.md
index 9eaf52358..184ede117 100644
--- a/src/doc/src/reference/registries.md
+++ b/src/doc/src/reference/registries.md
@@ -546,7 +546,9 @@ A successful response includes the JSON object:
 ```javascript
 {
     // Indicates the remove succeeded, always true.
-    "ok": true
+    "ok": true,
+    // A string to be displayed to the user.
+    "msg": "user someone has been deleted from owners of crate cargo"
 }
 ```
 
diff --git a/tests/testsuite/owner.rs b/tests/testsuite/owner.rs
index 0a7e7154b..d37206b20 100644
--- a/tests/testsuite/owner.rs
+++ b/tests/testsuite/owner.rs
@@ -6,12 +6,21 @@ use cargo_test_support::paths::CargoPathExt;
 use cargo_test_support::project;
 use cargo_test_support::registry::{self, api_path, registry_url};
 
-fn setup(name: &str) {
+fn setup(name: &str, content: Option<&str>) {
     let dir = api_path().join(format!("api/v1/crates/{}", name));
     dir.mkdir_p();
-    fs::write(
-        dir.join("owners"),
-        r#"{
+    match content {
+        Some(body) => {
+            fs::write(dir.join("owners"), body).unwrap();
+        }
+        None => {}
+    }
+}
+
+#[cargo_test]
+fn simple_list() {
+    registry::init();
+    let content = r#"{
         "users": [
             {
                 "id": 70,
@@ -19,15 +28,8 @@ fn setup(name: &str) {
                 "name": "Core"
             }
         ]
-    }"#,
-    )
-    .unwrap();
-}
-
-#[cargo_test]
-fn simple_list() {
-    registry::init();
-    setup("foo");
+    }"#;
+    setup("foo", Some(content));
 
     let p = project()
         .file(
@@ -48,3 +50,67 @@ fn simple_list() {
         .arg(registry_url().to_string())
         .run();
 }
+
+#[cargo_test]
+fn simple_add() {
+    registry::init();
+    setup("foo", None);
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.0.1"
+            authors = []
+            license = "MIT"
+            description = "foo"
+        "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("owner -a username --index")
+        .arg(registry_url().to_string())
+        .with_status(101)
+        .with_stderr(
+            "    Updating `[..]` index
+error: failed to invite owners to crate foo: response body is empty",
+        )
+        .run();
+}
+
+#[cargo_test]
+fn simple_remove() {
+    registry::init();
+    setup("foo", None);
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.0.1"
+            authors = []
+            license = "MIT"
+            description = "foo"
+        "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("owner -r username --index")
+        .arg(registry_url().to_string())
+        .with_status(101)
+        .with_stderr(
+            "    Updating `[..]` index
+       Owner removing [\"username\"] from crate foo
+error: failed to remove owners from crate foo
+
+Caused by:
+  response body is empty",
+        )
+        .run();
+}