diff --git a/CLAUDE.md b/CLAUDE.md
index e2860d3..efa544d 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -1,3 +1,9 @@
+<!--
+SPDX-FileCopyrightText: 2025 Adam Poulemanos <89049923+bashandbone@users.noreply.github.com>
+
+SPDX-License-Identifier: LicenseRef-PlainMIT OR MIT
+-->
+
 # CLAUDE.md
 
 This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
diff --git a/src/options.rs b/src/options.rs
index 9fb7a8f..5eaeb5e 100644
--- a/src/options.rs
+++ b/src/options.rs
@@ -402,13 +402,14 @@ impl Serialize for SerializableBranch {
 }
 
 impl<'de> Deserialize<'de> for SerializableBranch {
-    /// Deserialize from a plain string using the same logic as [`FromStr`].
+    /// Deserialize from a plain string, delegating to [`from_gitmodules`](GitmodulesConvert::from_gitmodules).
     /// Accepts `"."`, `"current"`, `"current-in-super-project"`, `"superproject"`, or `"super"`
-    /// as [`CurrentInSuperproject`](SerializableBranch::CurrentInSuperproject); all other strings
-    /// become [`Name`](SerializableBranch::Name).
+    /// as [`CurrentInSuperproject`](SerializableBranch::CurrentInSuperproject); all other
+    /// non-empty, non-whitespace strings become [`Name`](SerializableBranch::Name).
+    /// Empty or whitespace-only strings are rejected with a deserialization error.
     fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
         let s = String::deserialize(deserializer)?;
-        SerializableBranch::from_str(&s)
+        SerializableBranch::from_gitmodules(&s)
             .map_err(|_| serde::de::Error::custom(format!("invalid branch value: {s}")))
     }
 }
@@ -446,7 +447,10 @@ impl GitmodulesConvert for SerializableBranch {
             || options == "current-in-super-project"
             || options == "superproject"
             || options == "super"
-            || options == SerializableBranch::current_in_superproject().unwrap_or_default()
+            || SerializableBranch::current_in_superproject()
+                .ok()
+                .as_deref()
+                .map_or(false, |cur| cur == options)
         {
             return Ok(SerializableBranch::CurrentInSuperproject);
         }
@@ -464,6 +468,34 @@ impl GitmodulesConvert for SerializableBranch {
     }
 }
 
+#[cfg(test)]
+mod tests {
+    use super::SerializableBranch;
+
+    #[test]
+    fn test_branch_deserialize_from_toml_rejects_empty_and_whitespace() {
+        // Empty string should be rejected
+        let res_empty: Result<SerializableBranch, toml::de::Error> =
+            toml::from_str(r#"branch = """"#);
+        assert!(res_empty.is_err(), "expected error for empty branch value");
+        let err_empty = res_empty.unwrap_err().to_string();
+        assert!(
+            err_empty.contains("invalid branch value"),
+            "error for empty branch value should contain context, got: {err_empty}"
+        );
+
+        // Whitespace-only string should be rejected
+        let res_ws: Result<SerializableBranch, toml::de::Error> =
+            toml::from_str(r#"branch = "   ""#);
+        assert!(res_ws.is_err(), "expected error for whitespace-only branch value");
+        let err_ws = res_ws.unwrap_err().to_string();
+        assert!(
+            err_ws.contains("invalid branch value"),
+            "error for whitespace-only branch value should contain context, got: {err_ws}"
+        );
+    }
+}
+
 impl TryFrom<Branch> for SerializableBranch {
     type Error = ();