diff --git a/gitinspector/blame.py b/gitinspector/blame.py
index d284d89..8580fe9 100644
--- a/gitinspector/blame.py
+++ b/gitinspector/blame.py
@@ -156,12 +156,12 @@ class Blame(object):
 		for i in range(0, NUM_THREADS):
 			__thread_lock__.release()
 
-	def __add__(self, other):
-		if other == None:
-			return self
-
-		self.blames.update(other.blames)
-		return self
+	def __iadd__(self, other):
+		try:
+			self.blames.update(other.blames)
+			return self;
+		except AttributeError:
+			return other;
 
 	@staticmethod
 	def is_revision(string):
diff --git a/gitinspector/changes.py b/gitinspector/changes.py
index 4b95f89..1d1f620 100644
--- a/gitinspector/changes.py
+++ b/gitinspector/changes.py
@@ -230,19 +230,19 @@ class Changes(object):
 			self.last_commit_date = datetime.date(int(self.commits[-1].date[0:4]), int(self.commits[-1].date[5:7]),
 			                                      int(self.commits[-1].date[8:10]))
 
-	def __add__(self, other):
-		if other == None:
+	def __iadd__(self, other):
+		try:
+			self.authors.update(other.authors)
+			self.authors_dateinfo.update(other.authors_dateinfo)
+			self.authors_by_email.update(other.authors_by_email)
+			self.emails_by_author.update(other.emails_by_author)
+
+			for commit in other.commits:
+				bisect.insort(self.commits, commit)
+
 			return self
-
-		self.authors.update(other.authors)
-		self.authors_dateinfo.update(other.authors_dateinfo)
-		self.authors_by_email.update(other.authors_by_email)
-		self.emails_by_author.update(other.emails_by_author)
-
-		for commit in other.commits:
-			bisect.insort(self.commits, commit)
-
-		return self
+		except AttributeError:
+			return other;
 
 	def get_commits(self):
 		return self.commits
diff --git a/gitinspector/gitinspector.py b/gitinspector/gitinspector.py
index d8a19be..b725fb2 100644
--- a/gitinspector/gitinspector.py
+++ b/gitinspector/gitinspector.py
@@ -60,19 +60,19 @@ class Runner(object):
 		terminal.skip_escapes(not sys.stdout.isatty())
 		terminal.set_stdout_encoding()
 		previous_directory = os.getcwd()
-		summed_blames = None
-		summed_changes = None
-		summed_metrics = None
+		summed_blames = Blame.__new__(Blame)
+		summed_changes = Changes.__new__(Changes)
+		summed_metrics = MetricsLogic.__new__(MetricsLogic)
 
 		for repo in repos:
 			os.chdir(repo.location)
 			repo = repo if len(repos) > 1 else None
 			changes = Changes(repo, self.hard)
-			summed_blames = Blame(repo, self.hard, self.useweeks, changes) + summed_blames
-			summed_changes = changes + summed_changes
+			summed_blames += Blame(repo, self.hard, self.useweeks, changes)
+			summed_changes += changes
 
 			if self.include_metrics:
-				summed_metrics = MetricsLogic() + summed_metrics
+				summed_metrics += MetricsLogic()
 
 			if sys.stdout.isatty() and format.is_interactive_format():
 				terminal.clear_row()
@@ -80,7 +80,7 @@ class Runner(object):
 			os.chdir(previous_directory)
 
 		format.output_header(repos)
-		outputable.output(ChangesOutput(changes))
+		outputable.output(ChangesOutput(summed_changes))
 
 		if changes.get_commits():
 			outputable.output(BlameOutput(summed_changes, summed_blames))
diff --git a/gitinspector/metrics.py b/gitinspector/metrics.py
index d683e28..d4aeead 100644
--- a/gitinspector/metrics.py
+++ b/gitinspector/metrics.py
@@ -69,14 +69,14 @@ class MetricsLogic(object):
 				if lines > 0 and METRIC_CYCLOMATIC_COMPLEXITY_DENSITY_THRESHOLD < cycc / float(lines):
 					self.cyclomatic_complexity_density[i.strip()] = cycc / float(lines)
 
-	def __add__(self, other):
-		if other == None:
+	def __iadd__(self, other):
+		try:
+			self.eloc.update(other.eloc)
+			self.cyclomatic_complexity.update(other.cyclomatic_complexity)
+			self.cyclomatic_complexity_density.update(other.cyclomatic_complexity_density)
 			return self
-
-		self.eloc.update(other.eloc)
-		self.cyclomatic_complexity.update(other.cyclomatic_complexity)
-		self.cyclomatic_complexity_density.update(other.cyclomatic_complexity_density)
-		return self
+		except AttributeError:
+			return other;
 
 	@staticmethod
 	def get_cyclomatic_complexity(file_r, extension):