diff --git a/contrib/compile.cc b/contrib/compile.cc
index a98941e7..dba72328 100644
--- a/contrib/compile.cc
+++ b/contrib/compile.cc
@@ -1,6 +1,7 @@
 #include <sourcemeta/blaze/compiler.h>
 #include <sourcemeta/core/json.h>
 #include <sourcemeta/core/jsonpointer.h>
+#include <sourcemeta/core/jsonschema.h>
 #include <sourcemeta/core/options.h>
 
 #include <chrono>      // std::chrono
@@ -145,6 +146,20 @@ auto main(int argc, char **argv) noexcept -> int {
       document = std::move(extracted);
     }
 
+    // The compiler assumes valid schema input (object or boolean) and
+    // asserts otherwise. Guard here at the CLI boundary to ensure
+    // graceful failure instead of aborting on malformed inputs.
+    if (!sourcemeta::core::is_schema(document)) {
+      if (options.contains("path")) {
+        std::cerr << "error: the value at the given path is not a valid "
+                     "JSON Schema\n";
+      } else {
+        std::cerr << "error: the input is not a valid JSON Schema\n";
+      }
+
+      return EXIT_FAILURE;
+    }
+
     const auto compile_start{std::chrono::high_resolution_clock::now()};
     const auto schema_template{sourcemeta::blaze::compile(
         document, sourcemeta::core::schema_walker, resolver,
diff --git a/test/evaluator/evaluator_test.cc b/test/evaluator/evaluator_test.cc
index 3f5c866e..b83ae76b 100644
--- a/test/evaluator/evaluator_test.cc
+++ b/test/evaluator/evaluator_test.cc
@@ -314,3 +314,30 @@ TEST(Evaluator, format_assertion_vocabulary_unsupported) {
     FAIL() << "The compile function was expected to throw a vocabulary error";
   }
 }
+
+TEST(Evaluator, invalid_additional_properties_type) {
+  const sourcemeta::core::JSON schema{sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "type": "object",
+    "additionalProperties": 42
+  })JSON")};
+
+  EXPECT_THROW(
+      sourcemeta::blaze::compile(schema, sourcemeta::core::schema_walker,
+                                 sourcemeta::core::schema_resolver,
+                                 sourcemeta::blaze::default_schema_compiler),
+      sourcemeta::core::SchemaError);
+}
+
+TEST(Evaluator, invalid_items_type) {
+  const sourcemeta::core::JSON schema{sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "items": "invalid"
+  })JSON")};
+
+  EXPECT_THROW(
+      sourcemeta::blaze::compile(schema, sourcemeta::core::schema_walker,
+                                 sourcemeta::core::schema_resolver,
+                                 sourcemeta::blaze::default_schema_compiler),
+      sourcemeta::core::SchemaError);
+}