diff --git a/.changelog/d32ee107754148dba31cd1944f3ffcbf.json b/.changelog/d32ee107754148dba31cd1944f3ffcbf.json
new file mode 100644
index 00000000000..f823229025e
--- /dev/null
+++ b/.changelog/d32ee107754148dba31cd1944f3ffcbf.json
@@ -0,0 +1,8 @@
+{
+    "id": "d32ee107-7541-48db-a31c-d1944f3ffcbf",
+    "type": "bugfix",
+    "description": "Add client-side validation to ensure PutObject requests have a derivable content length.",
+    "modules": [
+        "service/s3"
+    ]
+}
\ No newline at end of file
diff --git a/codegen/smithy-aws-go-codegen/src/main/java/software/amazon/smithy/aws/go/codegen/customization/s3/ValidatePutObjectContentLength.java b/codegen/smithy-aws-go-codegen/src/main/java/software/amazon/smithy/aws/go/codegen/customization/s3/ValidatePutObjectContentLength.java
new file mode 100644
index 00000000000..05b92068dc6
--- /dev/null
+++ b/codegen/smithy-aws-go-codegen/src/main/java/software/amazon/smithy/aws/go/codegen/customization/s3/ValidatePutObjectContentLength.java
@@ -0,0 +1,33 @@
+package software.amazon.smithy.aws.go.codegen.customization.s3;
+
+import software.amazon.smithy.go.codegen.integration.GoIntegration;
+import software.amazon.smithy.go.codegen.integration.MiddlewareRegistrar;
+import software.amazon.smithy.go.codegen.integration.RuntimeClientPlugin;
+import software.amazon.smithy.model.shapes.ShapeId;
+
+import java.util.List;
+
+import static software.amazon.smithy.go.codegen.SymbolUtils.buildPackageSymbol;
+
+/**
+ * Adds validation to PutObject to ensure that content-length is derivable _somehow_ (either through the body being
+ * seekable or a length being set) - which is required for the operation to function since the service doesn't support
+ * chunked transfer-encoding.
+ */
+public class ValidatePutObjectContentLength implements GoIntegration {
+    private static final ShapeId PUT_OBJECT_SHAPE_ID = ShapeId.from("com.amazonaws.s3#PutObject");
+
+    private static final MiddlewareRegistrar MIDDLEWARE = MiddlewareRegistrar.builder()
+            .resolvedFunction(buildPackageSymbol("addValidatePutObjectContentLength"))
+            .build();
+
+    @Override
+    public List<RuntimeClientPlugin> getClientPlugins() {
+        return List.of(
+                RuntimeClientPlugin.builder()
+                        .operationPredicate((model, service, operation) -> operation.getId().equals(PUT_OBJECT_SHAPE_ID))
+                        .registerMiddleware(MIDDLEWARE)
+                        .build()
+        );
+    }
+}
diff --git a/codegen/smithy-aws-go-codegen/src/main/resources/META-INF/services/software.amazon.smithy.go.codegen.integration.GoIntegration b/codegen/smithy-aws-go-codegen/src/main/resources/META-INF/services/software.amazon.smithy.go.codegen.integration.GoIntegration
index 25a74f25eea..fb30b9427b1 100644
--- a/codegen/smithy-aws-go-codegen/src/main/resources/META-INF/services/software.amazon.smithy.go.codegen.integration.GoIntegration
+++ b/codegen/smithy-aws-go-codegen/src/main/resources/META-INF/services/software.amazon.smithy.go.codegen.integration.GoIntegration
@@ -83,3 +83,4 @@ software.amazon.smithy.aws.go.codegen.customization.AccountIDEndpointRouting
 software.amazon.smithy.aws.go.codegen.customization.RetryModeUserAgent
 software.amazon.smithy.aws.go.codegen.customization.RequestCompressionUserAgent
 software.amazon.smithy.aws.go.codegen.customization.s3.ExpressUserAgent
+software.amazon.smithy.aws.go.codegen.customization.s3.ValidatePutObjectContentLength
diff --git a/service/s3/api_op_PutObject.go b/service/s3/api_op_PutObject.go
index fffa96a7aba..400c4916b0a 100644
--- a/service/s3/api_op_PutObject.go
+++ b/service/s3/api_op_PutObject.go
@@ -716,6 +716,9 @@ func (c *Client) addOperationPutObjectMiddlewares(stack *middleware.Stack, optio
 	if err = addIsExpressUserAgent(stack); err != nil {
 		return err
 	}
+	if err = addValidatePutObjectContentLength(stack); err != nil {
+		return err
+	}
 	if err = addOpPutObjectValidationMiddleware(stack); err != nil {
 		return err
 	}
diff --git a/service/s3/put_object_content_length.go b/service/s3/put_object_content_length.go
new file mode 100644
index 00000000000..f28d6b3be9b
--- /dev/null
+++ b/service/s3/put_object_content_length.go
@@ -0,0 +1,55 @@
+package s3
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+
+	presignedurl "github.com/aws/aws-sdk-go-v2/service/internal/presigned-url"
+	"github.com/aws/smithy-go/middleware"
+)
+
+var errNoContentLength = errors.New(
+	"The operation input had an undefined content length. PutObject MUST have a " +
+		"derivable content length from either (1) an explicit value for the " +
+		"ContentLength input member (2) the Body input member implementing io.Seeker " +
+		"such that the SDK can derive a value.",
+)
+
+// PutObject MUST have a derivable content length for the body in some form,
+// since the service does not implement chunked transfer-encoding (and
+// aws-chunked encoding requires the length anyway).
+//
+// We gate this constraint at the client level through additional validation
+// rather than letting the request through, which would fail with a 501.
+type validatePutObjectContentLength struct{}
+
+func (*validatePutObjectContentLength) ID() string {
+	return "validatePutObjectContentLength"
+}
+
+func (*validatePutObjectContentLength) HandleInitialize(
+	ctx context.Context, in middleware.InitializeInput, next middleware.InitializeHandler,
+) (
+	out middleware.InitializeOutput, metadata middleware.Metadata, err error,
+) {
+	if presignedurl.GetIsPresigning(ctx) { // won't have a body
+		return next.HandleInitialize(ctx, in)
+	}
+
+	input, ok := in.Parameters.(*PutObjectInput)
+	if !ok {
+		return out, metadata, fmt.Errorf("unknown input parameters type %T", in.Parameters)
+	}
+
+	_, ok = input.Body.(io.Seeker)
+	if !ok && input.ContentLength == nil {
+		return out, metadata, errNoContentLength
+	}
+	return next.HandleInitialize(ctx, in)
+}
+
+func addValidatePutObjectContentLength(stack *middleware.Stack) error {
+	return stack.Initialize.Add(&validatePutObjectContentLength{}, middleware.After)
+}
diff --git a/service/s3/put_object_content_length_test.go b/service/s3/put_object_content_length_test.go
new file mode 100644
index 00000000000..4e6dd5e636b
--- /dev/null
+++ b/service/s3/put_object_content_length_test.go
@@ -0,0 +1,73 @@
+package s3
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"io"
+	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+)
+
+type reader struct {
+	p    []byte
+	read bool
+}
+
+func (r *reader) Read(p []byte) (int, error) {
+	if r.read {
+		return 0, io.EOF
+	}
+
+	r.read = true
+	copy(p, r.p)
+	return len(r.p), nil
+}
+
+func TestValidatePutObjectContentLength(t *testing.T) {
+	for name, cs := range map[string]struct {
+		Input     *PutObjectInput
+		ExpectErr bool
+	}{
+		"noseek,nolen": {
+			Input: &PutObjectInput{
+				Bucket: aws.String("bucket"),
+				Key:    aws.String("key"),
+				Body:   &reader{p: []byte("foo")},
+			},
+			ExpectErr: true,
+		},
+		"noseek,len": {
+			Input: &PutObjectInput{
+				Bucket:        aws.String("bucket"),
+				Key:           aws.String("key"),
+				Body:          &reader{p: []byte("foo")},
+				ContentLength: aws.Int64(3),
+			},
+			ExpectErr: false,
+		},
+		"seek,nolen": {
+			Input: &PutObjectInput{
+				Bucket: aws.String("bucket"),
+				Key:    aws.String("key"),
+				Body:   bytes.NewReader([]byte("foo")),
+			},
+			ExpectErr: false,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			svc := New(Options{
+				Region: "us-east-1",
+			})
+
+			_, err := svc.PutObject(context.Background(), cs.Input)
+			if cs.ExpectErr && !errors.Is(err, errNoContentLength) {
+				t.Errorf("expected errNoContentLength, got %v", err)
+			}
+			if !cs.ExpectErr && errors.Is(err, errNoContentLength) {
+				t.Errorf("expected no errNoContentLength but got it")
+			}
+		})
+	}
+}
diff --git a/service/s3/snapshot/api_op_PutObject.go.snap b/service/s3/snapshot/api_op_PutObject.go.snap
index e87107024e5..8a39ac451c9 100644
--- a/service/s3/snapshot/api_op_PutObject.go.snap
+++ b/service/s3/snapshot/api_op_PutObject.go.snap
@@ -5,6 +5,7 @@ PutObject
 		legacyEndpointContextSetter
 		S3Shared:ARNLookup
 		SetLogger
+		validatePutObjectContentLength
 		OperationInputValidation
 	Serialize stack step
 		putBucketContext