diff --git a/codegen-server-test/build.gradle.kts b/codegen-server-test/build.gradle.kts
index 5d9464b3a4..808d476058 100644
--- a/codegen-server-test/build.gradle.kts
+++ b/codegen-server-test/build.gradle.kts
@@ -21,8 +21,6 @@ val properties = PropertyRetriever(rootProject, project)
 val pluginName = "rust-server-codegen"
 val workingDirUnderBuildDir = "smithyprojections/codegen-server-test/"
 
-val checkedInSmithyRuntimeLockfile = rootProject.projectDir.resolve("rust-runtime/Cargo.lock")
-
 dependencies {
     implementation(project(":codegen-server"))
     implementation("software.amazon.smithy:smithy-aws-protocol-tests:$smithyVersion")
@@ -106,10 +104,9 @@ val allCodegenTests = "../codegen-core/common-test-models".let { commonModels ->
 project.registerGenerateSmithyBuildTask(rootProject, pluginName, allCodegenTests)
 project.registerGenerateCargoWorkspaceTask(rootProject, pluginName, allCodegenTests, workingDirUnderBuildDir)
 project.registerGenerateCargoConfigTomlTask(layout.buildDirectory.dir(workingDirUnderBuildDir).get().asFile)
-project.registerCopyCheckedInCargoLockfileTask(checkedInSmithyRuntimeLockfile, layout.buildDirectory.dir(workingDirUnderBuildDir).get().asFile)
 
 tasks["smithyBuild"].dependsOn("generateSmithyBuild")
-tasks["assemble"].finalizedBy("generateCargoWorkspace", "copyCheckedInCargoLockfile", "generateCargoConfigToml")
+tasks["assemble"].finalizedBy("generateCargoWorkspace", "generateCargoConfigToml")
 
 project.registerModifyMtimeTask()
 project.registerCargoCommandsTasks(layout.buildDirectory.dir(workingDirUnderBuildDir).get().asFile)
diff --git a/rust-runtime/aws-smithy-types/Cargo.toml b/rust-runtime/aws-smithy-types/Cargo.toml
index bf038a6464..e6093486c7 100644
--- a/rust-runtime/aws-smithy-types/Cargo.toml
+++ b/rust-runtime/aws-smithy-types/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "aws-smithy-types"
-version = "1.2.9"
+version = "1.2.10"
 authors = [
     "AWS Rust SDK Team <aws-sdk-rust@amazon.com>",
     "Russell Cohen <rcoh@amazon.com>",
diff --git a/rust-runtime/aws-smithy-types/src/date_time/format.rs b/rust-runtime/aws-smithy-types/src/date_time/format.rs
index 86ffd42ac7..33e27f5369 100644
--- a/rust-runtime/aws-smithy-types/src/date_time/format.rs
+++ b/rust-runtime/aws-smithy-types/src/date_time/format.rs
@@ -407,6 +407,12 @@ pub(crate) mod rfc3339 {
             )
             .into());
         }
+        if s.len() > 10 && !matches!(s.as_bytes()[10], b'T' | b't') {
+            return Err(DateTimeParseErrorKind::Invalid(
+                "RFC-3339 only allows `T` as a separator for date-time values".into(),
+            )
+            .into());
+        }
         let date_time = OffsetDateTime::parse(s, &Rfc3339).map_err(|err| {
             DateTimeParseErrorKind::Invalid(format!("invalid RFC-3339 date-time: {}", err).into())
         })?;
@@ -773,6 +779,43 @@ mod tests {
         http_date_check_roundtrip(9999999999, 0);
     }
 
+    #[test]
+    fn parse_rfc3339_invalid_separator() {
+        let test_cases = [
+            ("1985-04-12 23:20:50Z", AllowOffsets::OffsetsForbidden),
+            ("1985-04-12x23:20:50Z", AllowOffsets::OffsetsForbidden),
+            ("1985-04-12 23:20:50-02:00", AllowOffsets::OffsetsAllowed),
+            ("1985-04-12a23:20:50-02:00", AllowOffsets::OffsetsAllowed),
+        ];
+        for (date, offset) in test_cases.into_iter() {
+            let dt = rfc3339::parse(date, offset);
+            assert!(matches!(
+                dt.unwrap_err(),
+                DateTimeParseError {
+                    kind: DateTimeParseErrorKind::Invalid(_)
+                }
+            ));
+        }
+    }
+    #[test]
+    fn parse_rfc3339_t_separator() {
+        let test_cases = [
+            ("1985-04-12t23:20:50Z", AllowOffsets::OffsetsForbidden),
+            ("1985-04-12T23:20:50Z", AllowOffsets::OffsetsForbidden),
+            ("1985-04-12t23:20:50-02:00", AllowOffsets::OffsetsAllowed),
+            ("1985-04-12T23:20:50-02:00", AllowOffsets::OffsetsAllowed),
+        ];
+        for (date, offset) in test_cases.into_iter() {
+            let dt = rfc3339::parse(date, offset);
+            assert!(
+                dt.is_ok(),
+                "failed to parse date: '{}' with error: {:?}",
+                date,
+                dt.err().unwrap()
+            );
+        }
+    }
+
     proptest! {
         #![proptest_config(ProptestConfig::with_cases(10000))]