diff --git a/api/src/main/java/com/theokanning/openai/function/FunctionDefinition.java b/api/src/main/java/com/theokanning/openai/function/FunctionDefinition.java
index 150594b..84aec5b 100644
--- a/api/src/main/java/com/theokanning/openai/function/FunctionDefinition.java
+++ b/api/src/main/java/com/theokanning/openai/function/FunctionDefinition.java
@@ -113,6 +113,7 @@ public FunctionDefinition build() {
             }
             FunctionDefinition functionDefinition = new FunctionDefinition();
             functionDefinition.name = name;
+            functionDefinition.strict = strict;
             functionDefinition.description = description;
             functionDefinition.parametersDefinitionClass = parametersDefinitionClass;
             functionDefinition.parametersDefinition = parametersDefinition;
diff --git a/api/src/main/java/com/theokanning/openai/function/FunctionParametersSerializer.java b/api/src/main/java/com/theokanning/openai/function/FunctionParametersSerializer.java
index 87e9776..9924be3 100644
--- a/api/src/main/java/com/theokanning/openai/function/FunctionParametersSerializer.java
+++ b/api/src/main/java/com/theokanning/openai/function/FunctionParametersSerializer.java
@@ -29,6 +29,9 @@ public void serialize(FunctionDefinition value, JsonGenerator gen, SerializerPro
             parameterSchema.remove("$schema");
             parameterSchema.remove("title");
             parameterSchema.remove("additionalProperties");
+            if (Boolean.TRUE == value.getStrict()) {
+              parameterSchema.put("additionalProperties", Boolean.FALSE);
+            }
             gen.writeRawValue(JsonUtil.writeValueAsString(parameterSchema));
         } else {
             gen.writeFieldName("parameters");
diff --git a/api/src/test/java/com/theokanning/openai/FunctionDefinitionTest.java b/api/src/test/java/com/theokanning/openai/FunctionDefinitionTest.java
new file mode 100644
index 0000000..2cd328f
--- /dev/null
+++ b/api/src/test/java/com/theokanning/openai/FunctionDefinitionTest.java
@@ -0,0 +1,135 @@
+package com.theokanning.openai;
+
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.theokanning.openai.function.FunctionDefinition;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class FunctionDefinitionTest {
+
+    private final ObjectMapper objectMapper = new ObjectMapper();
+
+    class TestParameters {
+        public String name;
+    }
+
+    @Test
+    void shouldSerializeWithStrictTrue() throws Exception {
+        // given
+        FunctionDefinition function =
+                FunctionDefinition.builder()
+                        .name("test_function")
+                        .description("Test function")
+                        .strict(true)
+                        .build();
+
+        // when
+        String json = objectMapper.writeValueAsString(function);
+        JsonNode jsonNode = objectMapper.readTree(json);
+
+        // then
+        assertEquals(jsonNode.get("name").asText(), "test_function");
+        assertEquals(jsonNode.get("description").asText(),"Test function");
+        assertTrue(jsonNode.get("strict").asBoolean());
+    }
+
+    @Test
+    void shouldSerializeWithStrictFalse() throws Exception {
+        // given
+        FunctionDefinition function =
+                FunctionDefinition.builder()
+                        .name("test_function")
+                        .description("Test function")
+                        .strict(false)
+                        .build();
+
+        // when
+        String json = objectMapper.writeValueAsString(function);
+        JsonNode jsonNode = objectMapper.readTree(json);
+
+        // then
+        assertEquals("test_function", jsonNode.get("name").asText());
+        assertEquals("Test function", jsonNode.get("description").asText());
+        assertFalse(jsonNode.get("strict").asBoolean());
+    }
+
+    @Test
+    void shouldSerializeWithoutStrict() throws Exception {
+        // given
+        FunctionDefinition function =
+                FunctionDefinition.builder().name("test_function").description("Test function").build();
+
+        // when
+        String json = objectMapper.writeValueAsString(function);
+        JsonNode jsonNode = objectMapper.readTree(json);
+
+        // then
+        assertEquals("test_function", jsonNode.get("name").asText());
+        assertEquals("Test function", jsonNode.get("description").asText());
+        assertFalse(jsonNode.has("strict"));
+    }
+
+    @Test
+    void shouldSetAdditionalPropertiesFalseWhenStrictIsTrue() throws Exception {
+        // given
+        FunctionDefinition function =
+                FunctionDefinition.<TestParameters>builder()
+                        .name("test_function")
+                        .description("Test function")
+                        .strict(true)
+                        .parametersDefinitionByClass(TestParameters.class)
+                        .build();
+
+        // when
+        String json = objectMapper.writeValueAsString(function);
+        JsonNode jsonNode = objectMapper.readTree(json);
+        JsonNode parametersNode = jsonNode.get("parameters");
+
+        // then
+        assertFalse(parametersNode.get("additionalProperties").asBoolean());
+    }
+
+    @Test
+    void whenStrictIsFalse() throws Exception {
+        // given
+        FunctionDefinition function =
+                FunctionDefinition.<TestParameters>builder()
+                        .name("test_function")
+                        .description("Test function")
+                        .strict(false)
+                        .parametersDefinitionByClass(TestParameters.class)
+                        .build();
+
+        // when
+        String json = objectMapper.writeValueAsString(function);
+        JsonNode jsonNode = objectMapper.readTree(json);
+        JsonNode parametersNode = jsonNode.get("parameters");
+
+        // then
+        assertFalse(parametersNode.has("additionalProperties"));
+    }
+
+    @Test
+    void shouldNotSetAdditionalPropertiesWhenStrictIsNull() throws Exception {
+        // given
+        FunctionDefinition function =
+                FunctionDefinition.<TestParameters>builder()
+                        .name("test_function")
+                        .description("Test function")
+                        .parametersDefinitionByClass(TestParameters.class)
+                        .build();
+
+        // when
+        String json = objectMapper.writeValueAsString(function);
+        JsonNode jsonNode = objectMapper.readTree(json);
+        JsonNode parametersNode = jsonNode.get("parameters");
+
+        // then
+        assertFalse(parametersNode.has("additionalProperties"));
+    }
+}