diff --git a/lib/bugsnag/configuration.rb b/lib/bugsnag/configuration.rb
index 050305b8..9c7ccbfa 100644
--- a/lib/bugsnag/configuration.rb
+++ b/lib/bugsnag/configuration.rb
@@ -283,8 +283,10 @@ def initialize
       # Set up logging
       self.logger = Logger.new(STDOUT)
       self.logger.level = Logger::INFO
-      self.logger.formatter = proc do |severity, datetime, progname, msg|
-        "** #{progname} #{datetime}: #{msg}\n"
+      self.logger.formatter = proc do |_severity, datetime, _progname, msg|
+        message = msg.to_s
+        message = message[PROG_NAME.length..-1].sub(/\A:?\s*/, "") if message.start_with?(PROG_NAME)
+        "** #{PROG_NAME} #{datetime}: #{message}\n"
       end
 
       # Configure the bugsnag middleware stack
@@ -440,7 +442,7 @@ def clear_request_data
     #
     # @param message [String, #to_s] The message to log
     def info(message)
-      logger.info(PROG_NAME) { message }
+      logger.info(PROG_NAME) { format_log_message(message) }
     end
 
     ##
@@ -448,7 +450,7 @@ def info(message)
     #
     # @param message [String, #to_s] The message to log
     def warn(message)
-      logger.warn(PROG_NAME) { message }
+      logger.warn(PROG_NAME) { format_log_message(message) }
     end
 
     ##
@@ -456,7 +458,7 @@ def warn(message)
     #
     # @param message [String, #to_s] The message to log
     def error(message)
-      logger.error(PROG_NAME) { message }
+      logger.error(PROG_NAME) { format_log_message(message) }
     end
 
     ##
@@ -464,7 +466,7 @@ def error(message)
     #
     # @param message [String, #to_s] The message to log
     def debug(message)
-      logger.debug(PROG_NAME) { message }
+      logger.debug(PROG_NAME) { format_log_message(message) }
     end
 
     ##
@@ -764,6 +766,14 @@ def auto_track_sessions=(track_sessions)
 
     PROG_NAME = "[Bugsnag]"
 
+    def format_log_message(message)
+      message = message.to_s
+      return message if message.start_with?(PROG_NAME)
+      return PROG_NAME if message.empty?
+
+      "#{PROG_NAME} #{message}"
+    end
+
     def default_hostname
       # Send the heroku dyno name instead of hostname if available
       ENV["DYNO"] || Socket.gethostname;
diff --git a/spec/breadcrumbs/on_breadcrumb_callback_list_spec.rb b/spec/breadcrumbs/on_breadcrumb_callback_list_spec.rb
index 6011124a..1d81ebe1 100644
--- a/spec/breadcrumbs/on_breadcrumb_callback_list_spec.rb
+++ b/spec/breadcrumbs/on_breadcrumb_callback_list_spec.rb
@@ -246,8 +246,8 @@ def call(breadcrumb)
 
     message_index = 0
     expected_messages = [
-      /^Error occurred in on_breadcrumb callback: 'Oh no!'$/,
-      /^on_breadcrumb callback stacktrace:/
+      /^\[Bugsnag\] Error occurred in on_breadcrumb callback: 'Oh no!'$/,
+      /^\[Bugsnag\] on_breadcrumb callback stacktrace:/
     ]
 
     expect(logger).to have_received(:warn).with("[Bugsnag]").twice do |&block|
diff --git a/spec/breadcrumbs/validator_spec.rb b/spec/breadcrumbs/validator_spec.rb
index 99e0e101..44f2aea8 100644
--- a/spec/breadcrumbs/validator_spec.rb
+++ b/spec/breadcrumbs/validator_spec.rb
@@ -49,8 +49,8 @@
 
         expect(breadcrumb.ignore?).to eq(true)
 
-        expect(Bugsnag.configuration.logger).to have_received(:debug) do |&block|
-          expect(block.call).to eq("Automatic breadcrumb of type #{type} ignored: #{name}")
+        expect(Bugsnag.configuration.logger).to have_received(:debug).with("[Bugsnag]") do |&block|
+          expect(block.call).to eq("[Bugsnag] Automatic breadcrumb of type #{type} ignored: #{name}")
         end
       end
 
diff --git a/spec/bugsnag_spec.rb b/spec/bugsnag_spec.rb
index 328b15a6..3b3437cc 100644
--- a/spec/bugsnag_spec.rb
+++ b/spec/bugsnag_spec.rb
@@ -64,11 +64,11 @@
       end
 
       expected_messages = [
-        /^Error in notify block: This is the error message$/,
-        /^Error in notify block stacktrace: \[/
+        /^\[Bugsnag\] Error in notify block: This is the error message$/,
+        /^\[Bugsnag\] Error in notify block stacktrace: \[/
       ].each
 
-      expect(Bugsnag.configuration.logger).to have_received(:warn).with('[Bugsnag]').twice do |&block|
+      expect(Bugsnag.configuration.logger).to have_received(:warn).with("[Bugsnag]").twice do |&block|
         expect(block.call).to match(expected_messages.next)
       end
 
@@ -84,11 +84,11 @@
       end
 
       expected_messages = [
-        /^Error in internal notify block: This is an auto_notify error$/,
-        /^Error in internal notify block stacktrace: \[/
+        /^\[Bugsnag\] Error in internal notify block: This is an auto_notify error$/,
+        /^\[Bugsnag\] Error in internal notify block stacktrace: \[/
       ].each
 
-      expect(Bugsnag.configuration.logger).to have_received(:warn).with('[Bugsnag]').twice do |&block|
+      expect(Bugsnag.configuration.logger).to have_received(:warn).with("[Bugsnag]").twice do |&block|
         expect(block.call).to match(expected_messages.next)
       end
 
diff --git a/spec/configuration_spec.rb b/spec/configuration_spec.rb
index da2ac311..d184637c 100644
--- a/spec/configuration_spec.rb
+++ b/spec/configuration_spec.rb
@@ -364,8 +364,8 @@
   describe "logger" do
     before do
       @output = StringIO.new
-      @formatter = proc do |severity, _datetime, progname, message|
-        "#{progname} #{severity}: #{message}"
+      @formatter = proc do |severity, _datetime, _progname, message|
+        "#{severity}: #{message}"
       end
 
       logger = Logger.new(@output)
@@ -379,6 +379,47 @@ def output_lines
       @output.readlines.map(&:chomp) # old rubies don't support `readlines(chomp: true)`
     end
 
+    it "preserves the default log format" do
+      datetime = Time.utc(2026, 9, 6)
+      output = subject.logger.formatter.call(
+        "INFO", datetime, nil, "[Bugsnag] Info message"
+      )
+
+      expect(output).to eq("** [Bugsnag] #{datetime}: Info message\n")
+      expect(subject.logger.formatter.call("INFO", datetime, nil, "[Bugsnag]: Info message")).to eq(
+        "** [Bugsnag] #{datetime}: Info message\n"
+      )
+      expect(subject.logger.formatter.call("INFO", datetime, nil, "[Bugsnag]")).to eq(
+        "** [Bugsnag] #{datetime}: \n"
+      )
+    end
+
+    it "sets the Bugsnag progname on the logger as well as the message" do
+      logger = double("logger")
+      subject.logger = logger
+
+      %i[info warn error debug].each do |level|
+        expect(logger).to receive(level).with("[Bugsnag]") do |_progname, &block|
+          expect(block.call).to eq("[Bugsnag] #{level} message")
+        end
+
+        subject.public_send(level, "#{level} message")
+      end
+    end
+
+    it "does not leave a trailing space when the message is empty" do
+      logger = double("logger")
+      subject.logger = logger
+
+      [nil, ""].each do |message|
+        expect(logger).to receive(:info).with("[Bugsnag]") do |_progname, &block|
+          expect(block.call).to eq("[Bugsnag]")
+        end
+
+        subject.info(message)
+      end
+    end
+
     context "using configure" do
       before do
         Bugsnag.configuration.api_key = nil
@@ -398,7 +439,7 @@ def output_lines
 
           expect(output_lines.length).to be(1)
           expect(output_lines.first).to eq(
-            '[Bugsnag] WARN: No valid API key has been set, notifications will not be sent'
+            'WARN: [Bugsnag] No valid API key has been set, notifications will not be sent'
           )
         end
 
@@ -407,7 +448,7 @@ def output_lines
 
           expect(output_lines.length).to be(1)
           expect(output_lines.first).to eq(
-            '[Bugsnag] WARN: No valid API key has been set, notifications will not be sent'
+            'WARN: [Bugsnag] No valid API key has been set, notifications will not be sent'
           )
         end
       end
@@ -428,7 +469,7 @@ def output_lines
 
           expect(output_lines.length).to be(1)
           expect(output_lines.first).to eq(
-            '[Bugsnag] WARN: No valid API key has been set, notifications will not be sent'
+            'WARN: [Bugsnag] No valid API key has been set, notifications will not be sent'
           )
         end
 
@@ -457,7 +498,7 @@ def output_lines
       Bugsnag.configuration.info("Info message")
 
       expect(output_lines.length).to be(1)
-      expect(output_lines.first).to eq('[Bugsnag] INFO: Info message')
+      expect(output_lines.first).to eq('INFO: [Bugsnag] Info message')
     end
 
     it "should log warning messages to the set logger" do
@@ -466,7 +507,7 @@ def output_lines
       Bugsnag.configuration.warn("Warning message")
 
       expect(output_lines.length).to be(1)
-      expect(output_lines.first).to eq('[Bugsnag] WARN: Warning message')
+      expect(output_lines.first).to eq('WARN: [Bugsnag] Warning message')
     end
 
     it "should log error messages to the set logger" do
@@ -475,7 +516,7 @@ def output_lines
       Bugsnag.configuration.error("Error message")
 
       expect(output_lines.length).to be(1)
-      expect(output_lines.first).to eq('[Bugsnag] ERROR: Error message')
+      expect(output_lines.first).to eq('ERROR: [Bugsnag] Error message')
     end
 
     it "should log debug messages to the set logger" do
@@ -484,7 +525,14 @@ def output_lines
       Bugsnag.configuration.debug("Debug message")
 
       expect(output_lines.length).to be(1)
-      expect(output_lines.first).to eq('[Bugsnag] DEBUG: Debug message')
+      expect(output_lines.first).to eq('DEBUG: [Bugsnag] Debug message')
+    end
+
+    it "does not duplicate an existing Bugsnag prefix" do
+      Bugsnag.configuration.info("[Bugsnag] Info message")
+
+      expect(output_lines.length).to be(1)
+      expect(output_lines.first).to eq('INFO: [Bugsnag] Info message')
     end
   end
 
diff --git a/spec/integrations/logger_spec.rb b/spec/integrations/logger_spec.rb
index 6fbe49e4..7b444863 100644
--- a/spec/integrations/logger_spec.rb
+++ b/spec/integrations/logger_spec.rb
@@ -8,7 +8,7 @@
   end
 
   context 'in a Rails app' do
-    key_warning = '[Bugsnag]: No valid API key has been set, notifications will not be sent'
+    key_warning = '[Bugsnag] No valid API key has been set, notifications will not be sent'
     is_jruby = defined?(RUBY_ENGINE) && RUBY_ENGINE == 'jruby'
     incompatible = (RUBY_VERSION < '2.0.0') || is_jruby
 
diff --git a/spec/on_error_spec.rb b/spec/on_error_spec.rb
index 798befd1..017f5697 100644
--- a/spec/on_error_spec.rb
+++ b/spec/on_error_spec.rb
@@ -199,7 +199,7 @@
     expect(called_count).to be(2)
 
     expect(logger).to have_received(:debug).with("[Bugsnag]") do |&block|
-      expect(block.call).to eq("Not notifying RuntimeError due to ignore being signified in user provided middleware")
+      expect(block.call).to eq("[Bugsnag] Not notifying RuntimeError due to ignore being signified in user provided middleware")
     end
   end
 
@@ -257,8 +257,8 @@
 
     message_index = 0
     expected_messages = [
-      /^Error occurred in on_error callback: 'bad things'$/,
-      /^on_error callback stacktrace:/
+      /^\[Bugsnag\] Error occurred in on_error callback: 'bad things'$/,
+      /^\[Bugsnag\] on_error callback stacktrace:/
     ]
 
     expect(logger).to have_received(:warn).with("[Bugsnag]").twice do |&block|
diff --git a/spec/session_tracker_spec.rb b/spec/session_tracker_spec.rb
index 81bcb657..9e646c37 100644
--- a/spec/session_tracker_spec.rb
+++ b/spec/session_tracker_spec.rb
@@ -117,6 +117,21 @@
     expect(payload["sessionCounts"].size).to eq(1)
   end
 
+  it 'attributes invalid API key delivery failures to Bugsnag' do
+    output = StringIO.new
+    logger = Logger.new(output)
+    logger.formatter = proc do |_severity, _datetime, _progname, message|
+      message
+    end
+    Bugsnag.configuration.logger = logger
+    allow(Bugsnag.configuration).to receive(:valid_api_key?).and_return(false)
+
+    Bugsnag.start_session
+    Bugsnag.session_tracker.send_sessions
+
+    expect(output.string).to eq('[Bugsnag] Not delivering sessions due to an invalid api_key')
+  end
+
   it 'sets details from config' do
     Bugsnag.configure do |conf|
       conf.auto_capture_sessions = true