diff --git a/spec/profile_spec.cr b/spec/profile_spec.cr
index 272584f..5f0206c 100644
--- a/spec/profile_spec.cr
+++ b/spec/profile_spec.cr
@@ -74,5 +74,25 @@ module Dayoff::Test
       expected = 8 * 3 - 10 * 2
       expected.should eq span.total_hours
     end
+
+    it "not start twice" do
+      prof = create_profile
+      start_time = t(3, 10, 0)
+      prof.start start_time
+      expect_raises(AlreadyStarted) do
+        prof.start start_time
+      end
+    end
+
+    it "not finish twice" do
+      prof = create_profile
+      start_time = t(3, 10, 0)
+      finish_time = t(3, 20, 0)
+      prof.start start_time
+      prof.finish finish_time
+      expect_raises(StartedRecordNotFound) do
+        prof.finish finish_time
+      end
+    end
   end
 end
diff --git a/src/dayoff/exceptions.cr b/src/dayoff/exceptions.cr
index 0399476..5e5eb22 100644
--- a/src/dayoff/exceptions.cr
+++ b/src/dayoff/exceptions.cr
@@ -4,4 +4,7 @@ module Dayoff
 
   class StartedRecordNotFound < Exception
   end
+
+  class AlreadyStarted < Exception
+  end
 end
diff --git a/src/dayoff/profile.cr b/src/dayoff/profile.cr
index 02f6eca..dba2698 100644
--- a/src/dayoff/profile.cr
+++ b/src/dayoff/profile.cr
@@ -35,6 +35,9 @@ module Dayoff
     end
 
     def start(time : Time) : Nil
+      if started_point
+        raise AlreadyStarted.new
+      end
       @wrecords.each do |wr|
         if time <= wr.start || time <= wr.finish!
           raise CrossedTimeSpan.new
@@ -46,7 +49,7 @@ module Dayoff
     end
 
     def finish(time : Time) : Nil
-      started = @wrecords.find { |x| x.started? }
+      started = started_point
       if started.nil?
         raise StartedRecordNotFound.new
       end
@@ -59,5 +62,9 @@ module Dayoff
       worked = get_work_hours on_time
       planned - worked
     end
+
+    private def started_point
+      @wrecords.find { |x| x.started? }
+    end
   end
 end