diff --git a/src/codecTools/toJsonSchema.ts b/src/codecTools/toJsonSchema.ts
index 4a6d77a..c031420 100644
--- a/src/codecTools/toJsonSchema.ts
+++ b/src/codecTools/toJsonSchema.ts
@@ -25,6 +25,7 @@ type MappableType =
 
 /**
  * Convert an io-ts codec to a JSON Schema (v7)
+ *
  * @param _type - an io-ts codec
  * @param strict - whether to enable strict mode
  * @param alwaysIncludeRequired - whether to always include required fields (OpenAI requires this)
@@ -63,13 +64,28 @@ export const toJsonSchema = (
       ),
     };
   }
-  if (type._tag === 'IntersectionType') {
+  if (type._tag === 'IntersectionType' && !alwaysIncludeRequired) {
     return {
       allOf: type.types.map((t: any) =>
         toJsonSchema(t, strict, alwaysIncludeRequired),
       ),
     };
   }
+  if (type._tag === 'IntersectionType' && alwaysIncludeRequired) {
+    const results = type.types.map((t: any) =>
+      toJsonSchema(t, strict, alwaysIncludeRequired),
+    );
+    if (!results.every((r) => r.type === 'object')) {
+      throw new Error('InterfaceType must have all children as type=object');
+    }
+    return {
+      type: 'object',
+      required: results.map((r) => r.required).flat(),
+      properties: results.reduce((acc, r) => ({ ...acc, ...r.properties }), {}),
+      ...(strict ? { additionalProperties: false } : {}),
+    };
+  }
+
   if (type._tag === 'InterfaceType') {
     return {
       type: 'object',