From 06d760e33d1f13d7cdf6cb656a78139d80249d94 Mon Sep 17 00:00:00 2001
From: Sai Asish Y <say.apm35@gmail.com>
Date: Wed, 13 May 2026 13:46:54 -0700
Subject: [PATCH 1/2] test: capture missing nested-segment case conversion in
 Environment

---
 tests/testsuite/env.rs | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/tests/testsuite/env.rs b/tests/testsuite/env.rs
index 58d3d575..cb0b605e 100644
--- a/tests/testsuite/env.rs
+++ b/tests/testsuite/env.rs
@@ -574,6 +574,39 @@ fn test_parse_nested_kebab() {
     );
 }
 
+#[test]
+#[cfg(feature = "convert-case")]
+#[should_panic = "missing configuration field"]
+fn test_parse_nested_upper_camel() {
+    use config::Case;
+
+    #[derive(Deserialize, Debug)]
+    struct TestConfig {
+        #[serde(rename = "Otel")]
+        otel: Inner,
+    }
+
+    #[derive(Deserialize, Debug)]
+    struct Inner {
+        #[serde(rename = "Endpoint")]
+        endpoint: String,
+    }
+
+    temp_env::with_var("CONFIG_OTEL__ENDPOINT", Some("from env"), || {
+        let environment = Environment::default()
+            .prefix("CONFIG")
+            .prefix_separator("_")
+            .separator("__")
+            .convert_case(Case::UpperCamel);
+
+        let config = Config::builder().add_source(environment).build().unwrap();
+
+        let config: TestConfig = config.try_deserialize().unwrap();
+
+        assert_eq!(config.otel.endpoint, "from env");
+    });
+}
+
 #[test]
 fn test_parse_string() {
     // using a struct in an enum here to make serde use `deserialize_any`

From c2920ac686a408af8e03462c845263feb18ab09f Mon Sep 17 00:00:00 2001
From: Sai Asish Y <say.apm35@gmail.com>
Date: Wed, 13 May 2026 13:48:08 -0700
Subject: [PATCH 2/2] fix(env): apply convert_case to each nested key segment

---
 CHANGELOG.md           | 4 ++++
 src/env.rs             | 6 +++++-
 tests/testsuite/env.rs | 1 -
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5a8899f6..e0c8d2bb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/).
 <!-- next-header -->
 ## [Unreleased] - ReleaseDate
 
+### Fixes
+
+- `Environment::convert_case` now applies the case conversion to each nested key segment
+
 ## [0.15.22] - 2026-03-17
 
 ### Documentation
diff --git a/src/env.rs b/src/env.rs
index c647da30..b78c7e53 100644
--- a/src/env.rs
+++ b/src/env.rs
@@ -296,7 +296,11 @@ impl Source for Environment {
 
             #[cfg(feature = "convert-case")]
             if let Some(convert_case) = convert_case {
-                key = key.to_case(*convert_case);
+                key = key
+                    .split('.')
+                    .map(|segment| segment.to_case(*convert_case))
+                    .collect::<Vec<_>>()
+                    .join(".");
             }
 
             let value = if self.try_parsing {
diff --git a/tests/testsuite/env.rs b/tests/testsuite/env.rs
index cb0b605e..e83a0947 100644
--- a/tests/testsuite/env.rs
+++ b/tests/testsuite/env.rs
@@ -576,7 +576,6 @@ fn test_parse_nested_kebab() {
 
 #[test]
 #[cfg(feature = "convert-case")]
-#[should_panic = "missing configuration field"]
 fn test_parse_nested_upper_camel() {
     use config::Case;