diff --git a/lib/rage/sse/application.rb b/lib/rage/sse/application.rb
index 19b3e555..2aa1d057 100644
--- a/lib/rage/sse/application.rb
+++ b/lib/rage/sse/application.rb
@@ -54,5 +54,8 @@ def start_formatted_stream(connection)
 
   def start_raw_stream(connection)
     @stream.call(Rage::SSE::ConnectionProxy.new(connection))
+  rescue => e
+    connection.close if connection.open?
+    raise e
   end
 end
diff --git a/spec/sse/application_spec.rb b/spec/sse/application_spec.rb
new file mode 100644
index 00000000..7c08d31e
--- /dev/null
+++ b/spec/sse/application_spec.rb
@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+RSpec.describe Rage::SSE::Application do
+  let(:connection) { MockSSEConnection.new }
+
+  class MockSSEConnection
+    attr_reader :messages
+
+    def initialize
+      @messages = []
+      @open = true
+    end
+
+    def write(data)
+      @messages << data
+    end
+
+    def close
+      @open = false
+    end
+
+    def open?
+      @open
+    end
+  end
+
+  describe "#start_raw_stream" do
+    it "closes the connection when the proc raises an exception" do
+      failing_proc = ->(conn) {
+        conn.write("data: before error\n\n")
+        raise "boom"
+      }
+
+      app = described_class.new(failing_proc)
+
+      expect {
+        app.send(:start_raw_stream, connection)
+      }.to raise_error(RuntimeError, "boom")
+
+      expect(connection.open?).to be false
+    end
+
+    it "does not close the connection on normal completion" do
+      async_proc = ->(conn) {
+        conn.write("data: started\n\n")
+        # Proc returns without closing — a background fiber will close later
+      }
+
+      app = described_class.new(async_proc)
+      app.send(:start_raw_stream, connection)
+
+      expect(connection.open?).to be true
+    end
+
+    it "does not interfere when the proc closes the connection itself" do
+      well_behaved_proc = ->(conn) {
+        conn.write("data: hello\n\n")
+        conn.close
+      }
+
+      app = described_class.new(well_behaved_proc)
+      app.send(:start_raw_stream, connection)
+
+      expect(connection.open?).to be false
+      expect(connection.messages).to eq(["data: hello\n\n"])
+    end
+  end
+end