diff --git a/Cargo.toml b/Cargo.toml
index 53de677..9fa971e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "jtd"
-version = "0.1.1"
+version = "0.1.2"
 description = "A Rust implementation of JSON Type Definition"
 authors = ["JSON Type Definition Contributors"]
 edition = "2018"
diff --git a/json-typedef-spec b/json-typedef-spec
index af1e463..7108b38 160000
--- a/json-typedef-spec
+++ b/json-typedef-spec
@@ -1 +1 @@
-Subproject commit af1e4637944c79b21efbefc37506eadc2527132b
+Subproject commit 7108b38558a5107663a07a83b7fd8b2f45f63a6c
diff --git a/src/schema.rs b/src/schema.rs
index bce0b10..000d536 100644
--- a/src/schema.rs
+++ b/src/schema.rs
@@ -24,6 +24,7 @@ pub enum ValidateError {
     NonRootDefinitions,
     EmptyEnum,
     RepeatedProperty(String),
+    MappingNullable,
     MappingNotPropertiesForm,
 }
 
@@ -139,8 +140,15 @@ impl Schema {
 
                     match &schema.form {
                         form::Form::Properties(form::Properties {
-                            required, optional, ..
+                            required,
+                            optional,
+                            nullable,
+                            ..
                         }) => {
+                            if *nullable {
+                                return Err(ValidateError::MappingNullable);
+                            }
+
                             if required.contains_key(discriminator)
                                 || optional.contains_key(discriminator)
                             {