diff --git a/lib/stackprof/report.rb b/lib/stackprof/report.rb
index 523646b3..18729256 100644
--- a/lib/stackprof/report.rb
+++ b/lib/stackprof/report.rb
@@ -358,49 +358,70 @@ def print_file(filter, f = STDOUT)
     end
 
     def +(other)
-      raise ArgumentError, "cannot combine #{other.class}" unless self.class == other.class
-      raise ArgumentError, "cannot combine #{modeline} with #{other.modeline}" unless modeline == other.modeline
-      raise ArgumentError, "cannot combine v#{version} with v#{other.version}" unless version == other.version
-
-      f1, f2 = normalized_frames, other.normalized_frames
-      frames = (f1.keys + f2.keys).uniq.inject(Hash.new) do |hash, id|
-        if f1[id].nil?
-          hash[id] = f2[id]
-        elsif f2[id]
-          hash[id] = f1[id]
-          hash[id][:total_samples] += f2[id][:total_samples]
-          hash[id][:samples] += f2[id][:samples]
-          if f2[id][:edges]
-            edges = hash[id][:edges] ||= {}
-            f2[id][:edges].each do |edge, weight|
-              edges[edge] ||= 0
-              edges[edge] += weight
+      merge(other)
+    end
+
+    def merge(*others)
+      other_class = others.find {|o| o.class != self.class}
+      if other_class
+        raise ArgumentError, "cannot combine #{self.class} with #{other_class}"
+      end
+
+      other_modeline = others.find {|o| o.modeline != modeline}
+      if other_modeline
+        raise ArgumentError, "cannot combine #{modeline} with #{other_modeline}"
+      end
+
+      other_version = others.find {|o| o.version != version}
+      if other_version
+        raise ArgumentError, "cannot combine v#{version} with v#{other_version}"
+      end
+
+      all = [self] + others
+      merged = {}
+
+      all.each do |report|
+        report.normalized_frames.each do |id, frame|
+          if !merged[id]
+            merged[id] = frame
+            next
+          end
+
+          merged_frame = merged[id]
+
+          merged_frame[:total_samples] += frame[:total_samples]
+          merged_frame[:samples] += frame[:samples]
+
+          if frame[:edges]
+            merged_edges = (merged_frame[:edges] ||= {})
+            frame[:edges].each do |edge, weight|
+              merged_edges[edge] ||= 0
+              merged_edges[edge] += weight
             end
           end
-          if f2[id][:lines]
-            lines = hash[id][:lines] ||= {}
-            f2[id][:lines].each do |line, weight|
-              lines[line] = add_lines(lines[line], weight)
+
+          if frame[:lines]
+            merged_lines = (merged_frame[:lines] ||= {})
+            frame[:lines].each do |line, weight|
+              merged_lines[line] = add_lines(merged_lines[line], weight)
             end
           end
-        else
-          hash[id] = f1[id]
         end
-        hash
       end
 
-      d1, d2 = data, other.data
-      data = {
+      all_data = all.map(&:data)
+
+      new_data = {
         version: version,
-        mode: d1[:mode],
-        interval: d1[:interval],
-        samples: d1[:samples] + d2[:samples],
-        gc_samples: d1[:gc_samples] + d2[:gc_samples],
-        missed_samples: d1[:missed_samples] + d2[:missed_samples],
-        frames: frames
+        mode: data[:mode],
+        interval: data[:interval],
+        samples: all_data.map {|d| d[:samples]}.inject(:+),
+        gc_samples: all_data.map {|d| d[:gc_samples]}.inject(:+),
+        missed_samples: all_data.map {|d| d[:missed_samples]}.inject(:+),
+        frames: merged
       }
 
-      self.class.new(data)
+      self.class.new(new_data)
     end
 
     private
diff --git a/test/test_report.rb b/test/test_report.rb
index 6ca1536f..c1b536cc 100644
--- a/test/test_report.rb
+++ b/test/test_report.rb
@@ -2,7 +2,7 @@
 require 'stackprof'
 require 'minitest/autorun'
 
-class ReportDumpTest < MiniTest::Test
+class ReportTest < MiniTest::Test
   require 'stringio'
 
   def test_dump_to_stdout
@@ -26,8 +26,96 @@ def test_dump_to_file
     assert_dump data, f.string
   end
 
+  def test_merge
+    data = [
+      StackProf.run(mode: :cpu, raw: true) do
+        foo
+      end,
+      StackProf.run(mode: :cpu, raw: true) do
+        foo
+        bar
+      end,
+      StackProf.run(mode: :cpu, raw: true) do
+        foo
+        bar
+        baz
+      end
+    ]
+    expectations = {
+      foo: {
+        total_samples: 3,
+        samples: 3,
+        total_lines: 1,
+      },
+      bar: {
+        total_samples: 4,
+        samples: 2,
+        total_lines: 2,
+        has_boz_edge: true
+      },
+      baz: {
+        total_samples: 2,
+        samples: 1,
+        total_lines: 2,
+        has_boz_edge: true,
+      },
+      boz: {
+        total_samples: 3,
+        samples: 3,
+        total_lines: 1,
+      },
+    }
+
+    reports = data.map {|d| StackProf::Report.new(d)}
+    combined = reports[0].merge(*reports[1..-1])
+
+    frames = expectations.keys.inject(Hash.new) do |hash, key|
+      hash[key] = find_method_frame(combined, key)
+      hash
+    end
+
+    expectations.each do |key, expect|
+      frame = frames[key]
+      assert_equal expect[:total_samples], frame[:total_samples], key
+      assert_equal expect[:samples], frame[:samples], key
+
+      assert_equal expect[:total_lines], frame[:lines].length, key
+      assert_includes frame[:lines], frame[:line] + 1, key
+      assert_equal [expect[:samples], expect[:samples]], frame[:lines][frame[:line] + 1], key
+
+      if expect[:has_boz_edge]
+        assert_equal ({frames[:boz][:hash] => expect[:samples]}), frame[:edges]
+      end
+    end
+
+  end
+
   private
 
+  def find_method_frame(profile, name)
+    profile.frames.values.find do |frame|
+      frame[:name] == "ReportTest##{name}"
+    end
+  end
+
+  def foo
+    StackProf.sample
+  end
+
+  def bar
+    StackProf.sample
+    boz
+  end
+
+  def baz
+    StackProf.sample
+    boz
+  end
+
+  def boz
+    StackProf.sample
+  end
+
   def assert_dump(expected, marshal_data)
     assert_equal expected, Marshal.load(marshal_data)
   end