diff --git a/CHANGELOG.md b/CHANGELOG.md
index cfe170b..cdf6379 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 4.0.0
+  - Breaking: restrict unintended user constant usage [#56](https://github.com/logstash-plugins/logstash-filter-ruby/pull/56)
+  - Fix: do not handle potential fatal (Java) errors - let them propagate out
+
 ## 3.1.7
   - [DOC] Added docs to help people avoid concurrency issues (often caused by accidentally relying on shared state with global variables, constants, or unguarded overwriting of instance variables) [#58](https://github.com/logstash-plugins/logstash-filter-ruby/issues/58)
 
diff --git a/lib/logstash/filters/ruby.rb b/lib/logstash/filters/ruby.rb
index ff190f1..1dc77d7 100644
--- a/lib/logstash/filters/ruby.rb
+++ b/lib/logstash/filters/ruby.rb
@@ -60,7 +60,7 @@ def initialize(*params)
   def register
     if @code && @path.nil?
       eval(@init, binding, "(ruby filter init)") if @init
-      eval("define_singleton_method :filter_method do |event, &new_event_block|\n #{@code} \nend", binding, "(ruby filter code)")
+      eval("def self.filter_method(event, &new_event_block); #{@code} \nend", binding, "(ruby filter code)", 0)
     elsif @path && @code.nil?
       @script.register
     else
@@ -92,14 +92,9 @@ def filter(event, &block)
   def inline_script(event, &block)
     filter_method(event, &block)
     filter_matched(event)
-  rescue Exception => e
-    @logger.error("Ruby exception occurred: #{e.message}",
-                  :class     => e.class.name,
-                  :backtrace => e.backtrace)
-    if @tag_with_exception_message
-      event.tag("#{@tag_on_exception}: #{e}")
-    end
-    event.tag(@tag_on_exception)
+  rescue StandardError, ScriptError, java.lang.Exception => e
+    @logger.error("Exception occurred: #{e.message}", :exception => e.class, :backtrace => e.backtrace)
+    tag_exception(event, e)
   end
 
   def file_script(event)
@@ -108,22 +103,17 @@ def file_script(event)
       filter_matched(event)
 
       self.class.check_result_events!(results)
-    rescue => e
-      if @tag_with_exception_message
-        event.tag("#{@tag_on_exception}: #{e}")
-      end
-      event.tag(@tag_on_exception)
-      message = "Could not process event: " + e.message
-      @logger.error(message, :script_path => @path,
-                             :class => e.class.name,
-                             :backtrace => e.backtrace)
+    rescue StandardError, ScriptError, java.lang.Exception => e
+      @logger.error("Could not process event:", :message => e.message, :exception => e.class, :backtrace => e.backtrace,
+                    :script_path => @path)
+      tag_exception(event, e)
       return event
     end
 
     returned_original = false
     results.each do |r_event|
       # If the user has generated a new event we yield that for them here
-      if event == r_event
+      if event.equal? r_event
         returned_original = true
       else
         yield r_event
@@ -134,4 +124,13 @@ def file_script(event)
 
     event.cancel unless returned_original
   end
+
+  private
+
+  def tag_exception(event, e)
+    if @tag_with_exception_message
+      event.tag("#{@tag_on_exception}: #{e}")
+    end
+    event.tag(@tag_on_exception)
+  end
 end
diff --git a/logstash-filter-ruby.gemspec b/logstash-filter-ruby.gemspec
index 5c6a38f..45bef0f 100644
--- a/logstash-filter-ruby.gemspec
+++ b/logstash-filter-ruby.gemspec
@@ -1,7 +1,7 @@
 Gem::Specification.new do |s|
 
   s.name            = 'logstash-filter-ruby'
-  s.version         = '3.1.7'
+  s.version         = '4.0.0'
   s.licenses        = ['Apache License (2.0)']
   s.summary         = "Executes arbitrary Ruby code"
   s.description     = "This gem is a Logstash plugin required to be installed on top of the Logstash core pipeline using $LS_HOME/bin/logstash-plugin install gemname. This gem is not a stand-alone program"
@@ -23,6 +23,5 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency "logstash-core-plugin-api", ">= 1.60", "<= 2.99"
   s.add_development_dependency 'logstash-filter-date'
   s.add_development_dependency 'logstash-devutils'
-  s.add_development_dependency 'insist'
 end
 
diff --git a/spec/filters/ruby_spec.rb b/spec/filters/ruby_spec.rb
index 1806f82..45aded3 100644
--- a/spec/filters/ruby_spec.rb
+++ b/spec/filters/ruby_spec.rb
@@ -27,9 +27,9 @@
       sample("message" => "hello world", "mydate" => "2014-09-23T00:00:00-0800") do
         # json is rendered in pretty json since the JSON.pretty_generate created json from the event hash
         # pretty json contains \n
-        insist { subject.get("pretty").count("\n") } == 5
+        expect( subject.get("pretty").count("\n") ).to eql 5
         # usage of JSON.parse here is to avoid parser-specific order assertions
-        insist { JSON.parse(subject.get("pretty")) } == JSON.parse("{\n  \"message\": \"hello world\",\n  \"mydate\": \"2014-09-23T00:00:00-0800\",\n  \"@version\": \"1\",\n  \"@timestamp\": \"2014-09-23T08:00:00.000Z\"\n}")
+        expect( JSON.parse(subject.get("pretty")) ).to eql JSON.parse("{\n  \"message\": \"hello world\",\n  \"mydate\": \"2014-09-23T00:00:00-0800\",\n  \"@version\": \"1\",\n  \"@timestamp\": \"2014-09-23T08:00:00.000Z\"\n}")
       end
     end
 
@@ -54,9 +54,9 @@
       sample("message" => "hello world", "mydate" => "2014-09-23T00:00:00-0800") do
         # if this eventually breaks because we removed the custom to_json and/or added pretty support to JrJackson then all is good :)
         # non-pretty json does not contain \n
-        insist { subject.get("pretty").count("\n") } == 0
+        expect( subject.get("pretty").count("\n") ).to eql 0
         # usage of JSON.parse here is to avoid parser-specific order assertions
-        insist { JSON.parse(subject.get("pretty")) } == JSON.parse("{\"message\":\"hello world\",\"mydate\":\"2014-09-23T00:00:00-0800\",\"@version\":\"1\",\"@timestamp\":\"2014-09-23T08:00:00.000Z\"}")
+        expect( JSON.parse(subject.get("pretty")) ).to eql JSON.parse("{\"message\":\"hello world\",\"mydate\":\"2014-09-23T00:00:00-0800\",\"@version\":\"1\",\"@timestamp\":\"2014-09-23T08:00:00.000Z\"}")
       end
     end
 
@@ -79,8 +79,8 @@
       CONFIG
 
       sample("message" => "hello world", "mydate" => "2014-09-23T00:00:00-0800") do
-        insist { subject.get("mydate") } == "2014-09-23T00:00:00-0800"
-        insist { subject.get("tags") } == ["_rubyexception"]
+        expect( subject.get("mydate") ).to eql "2014-09-23T00:00:00-0800"
+        expect( subject.get("tags") ).to eql ["_rubyexception"]
       end
     end
 
@@ -114,6 +114,57 @@
         expect(subject.get("mydate")).to eq("2014-09-23T00:00:00-0800");
       end
     end
+
+    describe "code raising" do
+
+      let(:event) { LogStash::Event.new "message" => "hello world" }
+      let(:code) { 'raise "an_error"' }
+
+      subject(:filter) { ::LogStash::Filters::Ruby.new('code' => code) }
+      before(:each) { filter.register }
+
+      it "should handle (standard) error" do
+        expect( filter.logger ).to receive(:error).
+            with('Exception occurred: an_error', hash_including(:exception => RuntimeError)).
+            and_call_original
+
+        new_events = filter.multi_filter([event])
+        expect(new_events.length).to eq 1
+        expect(new_events[0]).to equal(event)
+        expect( event.get('tags') ).to eql [ '_rubyexception' ]
+      end
+
+      context 'fatal error' do
+
+        let(:code) { 'raise java.lang.AssertionError.new("TEST")' }
+
+        it "should not rescue Java errors" do
+          expect( filter.logger ).to_not receive(:error)
+
+          expect { filter.multi_filter([event]) }.to raise_error(java.lang.AssertionError)
+        end
+      end
+    end
+
+    describe "invalid script" do
+      let(:filter_params) { { 'code' => code } }
+      subject(:filter) { ::LogStash::Filters::Ruby.new(filter_params) }
+
+      let(:code) { 'sample do syntax error' }
+
+      it "should error out during register" do
+        expect { filter.register }.to raise_error(SyntaxError)
+      end
+
+      it "reports correct error line" do
+        begin
+          filter.register
+          fail('syntax error expected')
+        rescue SyntaxError => e
+          expect( e.message ).to match /\(ruby filter code\):1.*? unexpected end-of-file/
+        end
+      end
+    end
   end
 
   context "when using file based script" do
@@ -167,5 +218,39 @@
         expect {|b| filter.filter(incoming_event, &b) }.to yield_control.exactly(3).times
       end
     end
+
+    describe "script that raises" do
+      let(:script_filename) { 'raising.rb' }
+
+      before(:each) do
+        filter.register
+        incoming_event.set('error', 'ERR-MSG')
+      end
+
+      it "should handle (standard) error" do
+        expect( filter.logger ).to receive(:error).
+            with('Could not process event:', hash_including(:message => 'ERR-MSG', :exception => NameError)).
+            and_call_original
+        filter.filter(incoming_event)
+        expect( incoming_event.get('tags') ).to eql [ '_rubyexception' ]
+      end
+    end
+
+    describe "invalid .rb script" do
+      let(:script_filename) { 'invalid.rb' }
+
+      it "should error out during register" do
+        expect { filter.register }.to raise_error(SyntaxError)
+      end
+
+      it "should report correct line number" do
+        begin
+          filter.register
+          fail('syntax error expected')
+        rescue SyntaxError => e
+          expect( e.message ).to match /invalid\.rb\:7/
+        end
+      end
+    end
   end
 end
diff --git a/spec/fixtures/invalid.rb b/spec/fixtures/invalid.rb
new file mode 100644
index 0000000..43718d9
--- /dev/null
+++ b/spec/fixtures/invalid.rb
@@ -0,0 +1,8 @@
+# 1
+def register(params)
+  @params = params
+end
+# 5
+def invalid_syntax
+  Foo = :foo # on line 7
+end
\ No newline at end of file
diff --git a/spec/fixtures/raising.rb b/spec/fixtures/raising.rb
new file mode 100644
index 0000000..0fd4c19
--- /dev/null
+++ b/spec/fixtures/raising.rb
@@ -0,0 +1,7 @@
+def register(params)
+end
+
+def filter(event)
+  raise NameError, event.get('error') if event.get('error')
+  event
+end
\ No newline at end of file
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index c95e15c..dc64aba 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,3 +1,2 @@
 # encoding: utf-8
 require "logstash/devutils/rspec/spec_helper"
-require "insist"