diff --git a/src/ir/ir_default_compiler.h b/src/ir/ir_default_compiler.h
index c7edc38..745888f 100644
--- a/src/ir/ir_default_compiler.h
+++ b/src/ir/ir_default_compiler.h
@@ -19,7 +19,7 @@
       if (!allowed.contains(entry.first)) {                                    \
         throw sourcemeta::codegen::UnsupportedKeywordError(                    \
             (schema), (pointer), entry.first,                                  \
-            "Unexpected keyword in subschema");                                \
+            "Unsupported keyword in subschema");                               \
       }                                                                        \
     }                                                                          \
   }
@@ -497,8 +497,7 @@ auto default_compiler(const sourcemeta::core::JSON &schema,
     return handle_ref(schema, frame, location, vocabularies, resolver,
                       subschema);
   } else {
-    throw UnexpectedSchemaError(schema, location.pointer,
-                                "Unsupported subschema");
+    throw UnexpectedSchemaError(schema, location.pointer, "Unsupported schema");
   }
 }
 
diff --git a/test/ir/CMakeLists.txt b/test/ir/CMakeLists.txt
index 71da014..a91d037 100644
--- a/test/ir/CMakeLists.txt
+++ b/test/ir/CMakeLists.txt
@@ -1,6 +1,6 @@
 sourcemeta_googletest(NAMESPACE sourcemeta PROJECT codegen NAME ir
   FOLDER "Codegen/IR"
-  SOURCES ir_2020_12_test.cc ir_symbol_test.cc ir_test_utils.h)
+  SOURCES ir_test.cc ir_2020_12_test.cc ir_symbol_test.cc ir_test_utils.h)
 
 target_link_libraries(sourcemeta_codegen_ir_unit
   PRIVATE sourcemeta::codegen::ir)
diff --git a/test/ir/ir_test.cc b/test/ir/ir_test.cc
new file mode 100644
index 0000000..d7e7797
--- /dev/null
+++ b/test/ir/ir_test.cc
@@ -0,0 +1,71 @@
+#include <gtest/gtest.h>
+
+#include <sourcemeta/codegen/ir.h>
+#include <sourcemeta/core/jsonschema.h>
+
+TEST(IR, unsupported_dialect_draft3) {
+  const sourcemeta::core::JSON schema{sourcemeta::core::parse_json(R"JSON({
+    "$schema": "http://json-schema.org/draft-03/schema#",
+    "type": "string"
+  })JSON")};
+
+  EXPECT_THROW(
+      sourcemeta::codegen::compile(schema, sourcemeta::core::schema_walker,
+                                   sourcemeta::core::schema_resolver,
+                                   sourcemeta::codegen::default_compiler),
+      sourcemeta::core::SchemaVocabularyError);
+}
+
+TEST(IR, unsupported_keyword_error) {
+  const sourcemeta::core::JSON schema{sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "type": "string",
+    "if": { "minLength": 5 },
+    "then": { "maxLength": 10 }
+  })JSON")};
+
+  EXPECT_THROW(
+      sourcemeta::codegen::compile(schema, sourcemeta::core::schema_walker,
+                                   sourcemeta::core::schema_resolver,
+                                   sourcemeta::codegen::default_compiler),
+      sourcemeta::codegen::UnsupportedKeywordError);
+}
+
+TEST(IR, unsupported_keyword_value_error_type_not_string) {
+  const sourcemeta::core::JSON schema{sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "type": 123
+  })JSON")};
+
+  EXPECT_THROW(
+      sourcemeta::codegen::compile(schema, sourcemeta::core::schema_walker,
+                                   sourcemeta::core::schema_resolver,
+                                   sourcemeta::codegen::default_compiler),
+      sourcemeta::codegen::UnsupportedKeywordValueError);
+}
+
+TEST(IR, unsupported_keyword_value_error_unknown_type) {
+  const sourcemeta::core::JSON schema{sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "type": "foo"
+  })JSON")};
+
+  EXPECT_THROW(
+      sourcemeta::codegen::compile(schema, sourcemeta::core::schema_walker,
+                                   sourcemeta::core::schema_resolver,
+                                   sourcemeta::codegen::default_compiler),
+      sourcemeta::codegen::UnsupportedKeywordValueError);
+}
+
+TEST(IR, unexpected_schema_error_unsupported_shape) {
+  const sourcemeta::core::JSON schema{sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "not": { "type": "string" }
+  })JSON")};
+
+  EXPECT_THROW(
+      sourcemeta::codegen::compile(schema, sourcemeta::core::schema_walker,
+                                   sourcemeta::core::schema_resolver,
+                                   sourcemeta::codegen::default_compiler),
+      sourcemeta::codegen::UnexpectedSchemaError);
+}