diff --git a/aws/sdk/integration-tests/s3/tests/bucket-required.rs b/aws/sdk/integration-tests/s3/tests/bucket-required.rs
new file mode 100644
index 00000000000..7ef77310663
--- /dev/null
+++ b/aws/sdk/integration-tests/s3/tests/bucket-required.rs
@@ -0,0 +1,28 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+use aws_config::SdkConfig;
+use aws_credential_types::provider::SharedCredentialsProvider;
+use aws_sdk_s3::config::{Credentials, Region};
+use aws_sdk_s3::Client;
+use aws_smithy_client::test_connection::capture_request;
+
+#[tokio::test]
+async fn dont_dispatch_when_bucket_is_unset() {
+    let (conn, rcvr) = capture_request(None);
+    let sdk_config = SdkConfig::builder()
+        .credentials_provider(SharedCredentialsProvider::new(Credentials::for_tests()))
+        .region(Region::new("us-east-1"))
+        .http_connector(conn.clone())
+        .build();
+    let client = Client::new(&sdk_config);
+    let err = client
+        .list_objects_v2()
+        .send()
+        .await
+        .expect_err("bucket not set");
+    assert_eq!(format!("{}", err), "failed to construct request");
+    rcvr.expect_no_request();
+}
diff --git a/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/generators/EndpointParamsInterceptorGenerator.kt b/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/generators/EndpointParamsInterceptorGenerator.kt
index a2c8a581b71..c458a03706a 100644
--- a/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/generators/EndpointParamsInterceptorGenerator.kt
+++ b/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/generators/EndpointParamsInterceptorGenerator.kt
@@ -28,9 +28,11 @@ import software.amazon.smithy.rust.codegen.core.rustlang.withBlockTemplate
 import software.amazon.smithy.rust.codegen.core.rustlang.writable
 import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType
 import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType.Companion.preludeScope
+import software.amazon.smithy.rust.codegen.core.smithy.generators.OperationBuildError
 import software.amazon.smithy.rust.codegen.core.util.PANIC
 import software.amazon.smithy.rust.codegen.core.util.dq
 import software.amazon.smithy.rust.codegen.core.util.inputShape
+import software.amazon.smithy.rust.codegen.core.util.letIf
 import software.amazon.smithy.rust.codegen.core.util.orNull
 import software.amazon.smithy.rust.codegen.core.util.toPascalCase
 
@@ -134,8 +136,11 @@ class EndpointParamsInterceptorGenerator(
         // lastly, allow these to be overridden by members
         memberParams.forEach { (memberShape, param) ->
             val memberName = codegenContext.symbolProvider.toMemberName(memberShape)
-            rust(
-                ".${EndpointParamsGenerator.setterName(param.name)}(_input.$memberName.clone())",
+            val member = writable("_input.$memberName.clone()").letIf(memberShape.isRequired) { ref ->
+                OperationBuildError(codegenContext.runtimeConfig).emptyOrUnset(symbolProvider, ref, memberShape)
+            }
+            rustTemplate(
+                ".${EndpointParamsGenerator.setterName(param.name)}(dbg!(#{member}))", "member" to member,
             )
         }
     }
diff --git a/codegen-client/src/test/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/EndpointsDecoratorTest.kt b/codegen-client/src/test/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/EndpointsDecoratorTest.kt
index 1836a090bb6..d6878f1b96b 100644
--- a/codegen-client/src/test/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/EndpointsDecoratorTest.kt
+++ b/codegen-client/src/test/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/EndpointsDecoratorTest.kt
@@ -111,6 +111,7 @@ class EndpointsDecoratorTest {
 
         structure TestOperationInput {
             @contextParam(name: "Bucket")
+            @required
             bucket: String,
             nested: NestedStructure
         }
@@ -210,6 +211,10 @@ class EndpointsDecoratorTest {
                             interceptor.called.load(Ordering::Relaxed),
                             "the interceptor should have been called"
                         );
+
+                        // bucket_name is unset and marked as required on the model, so we'll refuse to construct this request
+                        let err = client.test_operation().send().await.expect_err("param missing");
+                        assert_eq!(format!("{}", err), "failed to construct request");
                     }
                     """,
                 )
diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGenerator.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGenerator.kt
index e86061c4c3c..0fa8dfa919c 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGenerator.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGenerator.kt
@@ -12,6 +12,7 @@ import software.amazon.smithy.model.shapes.MemberShape
 import software.amazon.smithy.model.shapes.StructureShape
 import software.amazon.smithy.rust.codegen.core.rustlang.Attribute
 import software.amazon.smithy.rust.codegen.core.rustlang.Attribute.Companion.derive
+import software.amazon.smithy.rust.codegen.core.rustlang.RustModule
 import software.amazon.smithy.rust.codegen.core.rustlang.RustType
 import software.amazon.smithy.rust.codegen.core.rustlang.RustWriter
 import software.amazon.smithy.rust.codegen.core.rustlang.Writable
@@ -77,9 +78,39 @@ fun RuntimeConfig.operationBuildError() = RuntimeType.operationModule(this).reso
 fun RuntimeConfig.serializationError() = RuntimeType.operationModule(this).resolve("error::SerializationError")
 
 class OperationBuildError(private val runtimeConfig: RuntimeConfig) {
+
+    fun emptyOrUnset(symbolProvider: SymbolProvider, ref: Writable, member: MemberShape): Writable {
+        val checkSet = RuntimeType.forInlineFun("check_set", RustModule.private("serde_util")) {
+            rustTemplate(
+                """
+                pub(crate) fn check_set<T: #{Default} + #{PartialEq}>(field: Option<T>, name: &'static str) -> Result<T, #{BuildError}> {
+                    if let Some(field) = field {
+                        if field != Default::default() {
+                            return Ok(field)
+                        }
+                    }
+                    Err(#{BuildError}::missing_field(name, "field was required"))
+                }
+
+                """,
+                "BuildError" to runtimeConfig.operationBuildError(), *preludeScope,
+            )
+        }
+
+        val fieldName = symbolProvider.toMemberName(member)
+        return writable {
+            rustTemplate(
+                "Some(#{checkSet}(#{ref}, ${fieldName.dq()})?)",
+                "checkSet" to checkSet,
+                "ref" to ref,
+            )
+        }
+    }
+
     fun missingField(field: String, details: String) = writable {
         rust("#T::missing_field(${field.dq()}, ${details.dq()})", runtimeConfig.operationBuildError())
     }
+
     fun invalidField(field: String, details: String) = invalidField(field) { rust(details.dq()) }
     fun invalidField(field: String, details: Writable) = writable {
         rustTemplate(
@@ -164,7 +195,8 @@ class BuilderGenerator(
     }
 
     private fun RustWriter.missingRequiredField(field: String) {
-        val detailedMessage = "$field was not specified but it is required when building ${symbolProvider.toSymbol(shape).name}"
+        val detailedMessage =
+            "$field was not specified but it is required when building ${symbolProvider.toSymbol(shape).name}"
         OperationBuildError(runtimeConfig).missingField(field, detailedMessage)(this)
     }