diff --git a/java/src/json/ext/GeneratorState.java b/java/src/json/ext/GeneratorState.java
index dabc9e255..3fdf4f276 100644
--- a/java/src/json/ext/GeneratorState.java
+++ b/java/src/json/ext/GeneratorState.java
@@ -545,43 +545,41 @@ public IRubyObject _configure(ThreadContext context, IRubyObject vOpts) {
         checkFrozen();
         OptionsReader opts = new OptionsReader(context, vOpts);
 
-        ByteList indent = opts.getString("indent");
-        if (indent != null) this.indent = indent;
-
-        ByteList space = opts.getString("space");
-        if (space != null) this.space = space;
-
-        ByteList spaceBefore = opts.getString("space_before");
-        if (spaceBefore != null) this.spaceBefore = spaceBefore;
-
-        ByteList arrayNl = opts.getString("array_nl");
-        if (arrayNl != null) this.arrayNl = arrayNl;
-
-        this.asJSON = opts.getProc("as_json");
-
-        ByteList objectNl = opts.getString("object_nl");
-        if (objectNl != null) this.objectNl = objectNl;
-
-        maxNesting = opts.getInt("max_nesting", DEFAULT_MAX_NESTING);
-        allowNaN   = opts.getBool("allow_nan",  DEFAULT_ALLOW_NAN);
-        asciiOnly  = opts.getBool("ascii_only", DEFAULT_ASCII_ONLY);
-        scriptSafe = opts.getBool("script_safe", DEFAULT_SCRIPT_SAFE);
-        strict = opts.getBool("strict", DEFAULT_STRICT);
-        bufferInitialLength = opts.getInt("buffer_initial_length", DEFAULT_BUFFER_INITIAL_LENGTH);
-
-        depth = opts.getInt("depth", 0);
+        this.indent = stringConfig(opts, "indent", this.indent);
+        this.space = stringConfig(opts, "space", this.space);
+        this.spaceBefore = stringConfig(opts, "space_before", this.spaceBefore);
+        this.arrayNl = stringConfig(opts, "array_nl", this.arrayNl);
+        this.objectNl = stringConfig(opts, "object_nl", this.objectNl);
+
+        if (opts.hasKey("as_json")) this.asJSON = opts.getProc("as_json");
+
+        maxNesting = opts.getInt("max_nesting", maxNesting);
+        allowNaN   = opts.getBool("allow_nan",  allowNaN);
+        asciiOnly  = opts.getBool("ascii_only", asciiOnly);
+        scriptSafe = opts.getBool("script_safe", scriptSafe);
+        strict = opts.getBool("strict", strict);
+        bufferInitialLength = opts.getInt("buffer_initial_length", bufferInitialLength);
+
+        depth = opts.getInt("depth", depth);
         if (depth < 0) {
             throw context.runtime.newArgumentError("depth must be >= 0 (got: " + depth + ")");
         }
-        this.allowDuplicateKey = opts.getBool("allow_duplicate_key", false);
+        this.allowDuplicateKey = opts.getBool("allow_duplicate_key", allowDuplicateKey);
 
-        sortKeys = normalizeSortKeys(context, opts.get("sort_keys"));
+        if (opts.hasKey("sort_keys")) sortKeys = normalizeSortKeys(context, opts.get("sort_keys"));
 
         opts.ensureEmpty();
 
         return this;
     }
 
+    // A falsy value writes the empty string, as string_config() does in the C extension.
+    private static ByteList stringConfig(OptionsReader opts, String key, ByteList current) {
+        if (!opts.hasKey(key)) return current;
+        ByteList value = opts.getString(key);
+        return value == null ? ByteList.EMPTY_BYTELIST : value;
+    }
+
     /**
      * <code>State#to_h()</code>
      *
diff --git a/test/json/json_generator_test.rb b/test/json/json_generator_test.rb
index 1f4b5d949..1b2197735 100755
--- a/test/json/json_generator_test.rb
+++ b/test/json/json_generator_test.rb
@@ -539,18 +539,32 @@ def test_configure_keeps_the_layout_of_a_pretty_state
   end
 
   def test_configure_only_writes_the_other_options_it_is_given
-    omit 'JRuby resets the non-string options' if RUBY_ENGINE == 'jruby'
-    state = JSON.state.new(max_nesting: 3, allow_nan: true, ascii_only: true, script_safe: true)
+    state = JSON.state.new(max_nesting: 3, allow_nan: true, ascii_only: true, script_safe: true,
+                           strict: true, buffer_initial_length: 32)
     state.configure(indent: '1')
     assert_equal '1', state.indent
     assert_equal 3, state.max_nesting
     assert_equal true, state.allow_nan?
     assert_equal true, state.ascii_only?
     assert_equal true, state.script_safe?
+    assert_equal true, state.strict?
+    assert_equal 32, state.buffer_initial_length
+  end
+
+  def test_configure_keeps_sort_keys
+    state = JSON.state.new(sort_keys: true)
+    state.configure(depth: 0)
+    assert_equal '{"a":2,"b":1}', state.generate({ 'b' => 1, 'a' => 2 })
+  end
+
+  def test_configure_keeps_as_json
+    as_json = ->(object, _is_key) { object.to_s }
+    state = JSON.state.new(strict: true, as_json: as_json)
+    state.configure(depth: 0)
+    assert_equal as_json, state.as_json
   end
 
   def test_configure_writes_a_string_option_given_as_nil
-    omit 'JRuby keeps the previous value for an explicit nil' if RUBY_ENGINE == 'jruby'
     state = JSON.state.new(indent: '1', space: '2')
     state.configure(indent: nil)
     assert_equal '', state.indent