diff --git a/lib/childprocess/abstract_process.rb b/lib/childprocess/abstract_process.rb
index 93fd064..f445223 100644
--- a/lib/childprocess/abstract_process.rb
+++ b/lib/childprocess/abstract_process.rb
@@ -181,7 +181,7 @@ def leader?
     end
 
     def log(*args)
-      ChildProcess.logger.debug "#{self.inspect} : #{args.inspect}"
+      ChildProcess.logger.debug "#{self.class}(pid=#{@pid.inspect}) : #{args.inspect}"
     end
 
     def assert_started
diff --git a/lib/childprocess/process_spawn_process.rb b/lib/childprocess/process_spawn_process.rb
index 11bd3a6..5c52cc6 100644
--- a/lib/childprocess/process_spawn_process.rb
+++ b/lib/childprocess/process_spawn_process.rb
@@ -43,8 +43,11 @@ def launch_process
         key = key.to_s
         value = value.nil? ? nil : value.to_s
 
-        if key.include?("\0") || key.include?("=") || value.to_s.include?("\0")
-          raise InvalidEnvironmentVariable, "#{key.inspect} => #{value.to_s.inspect}"
+        if key.include?("\0") || key.include?("=")
+          raise InvalidEnvironmentVariable, "invalid environment variable name: #{key.inspect}"
+        end
+        if value.to_s.include?("\0")
+          raise InvalidEnvironmentVariable, "invalid value for environment variable #{key.inspect}"
         end
         environment[key] = value
       end