diff --git a/codegen/smithy-dafny-codegen/src/main/java/software/amazon/polymorph/CodegenConstants.java b/codegen/smithy-dafny-codegen/src/main/java/software/amazon/polymorph/CodegenConstants.java
index 0383c1b56..bd9f20305 100644
--- a/codegen/smithy-dafny-codegen/src/main/java/software/amazon/polymorph/CodegenConstants.java
+++ b/codegen/smithy-dafny-codegen/src/main/java/software/amazon/polymorph/CodegenConstants.java
@@ -1,5 +1,5 @@
 package software.amazon.polymorph;
 
 public class CodegenConstants {
-    public static String DAFNY_DATETIME_STRING_FORMAT = "%Y-%m-%dT%H:%M:%S";
+    public static String DAFNY_DATETIME_STRING_FORMAT = "%Y-%m-%dT%H:%M:%S.%fZ";
 }
diff --git a/codegen/smithy-dafny-codegen/src/main/java/software/amazon/polymorph/smithypython/awssdk/shapevisitor/AwsSdkToDafnyShapeVisitor.java b/codegen/smithy-dafny-codegen/src/main/java/software/amazon/polymorph/smithypython/awssdk/shapevisitor/AwsSdkToDafnyShapeVisitor.java
index 2dcb95774..392536a73 100644
--- a/codegen/smithy-dafny-codegen/src/main/java/software/amazon/polymorph/smithypython/awssdk/shapevisitor/AwsSdkToDafnyShapeVisitor.java
+++ b/codegen/smithy-dafny-codegen/src/main/java/software/amazon/polymorph/smithypython/awssdk/shapevisitor/AwsSdkToDafnyShapeVisitor.java
@@ -246,7 +246,8 @@ public String enumShape(EnumShape shape) {
   @Override
   public String timestampShape(TimestampShape shape) {
     writer.addStdlibImport("_dafny");
-    return "_dafny.Seq(%1$s.strftime(\"%2$s\"))".formatted(
+    writer.addStdlibImport("datetime", "timezone");
+    return "_dafny.Seq(%1$s.astimezone(timezone.utc).strftime(\"%2$s\"))".formatted(
             dataSource,
             DAFNY_DATETIME_STRING_FORMAT
     );