diff --git a/codegen/src/main/java/software/amazon/awssdk/codegen/poet/model/ModelMethodOverrides.java b/codegen/src/main/java/software/amazon/awssdk/codegen/poet/model/ModelMethodOverrides.java
index dcba831d24b3..6418517dce8b 100644
--- a/codegen/src/main/java/software/amazon/awssdk/codegen/poet/model/ModelMethodOverrides.java
+++ b/codegen/src/main/java/software/amazon/awssdk/codegen/poet/model/ModelMethodOverrides.java
@@ -106,6 +106,10 @@ public MethodSpec equalsMethod(ShapeModel shapeModel) {
     }
 
     public MethodSpec toStringMethod(ShapeModel shapeModel) {
+        if (shapeModel == null) {
+            throw new IllegalArgumentException("shapeModel cannot be null");
+        }
+
         String javadoc = "Returns a string representation of this object. This is useful for testing and " +
                          "debugging. Sensitive data will be redacted from this string using a placeholder " +
                          "value. ";