--- a/mercurial/patch.py	Fri May 19 12:38:34 2017 +0200
+++ b/mercurial/patch.py	Wed May 17 20:51:17 2017 -0500
@@ -2654,19 +2654,28 @@
         if filename:
             results.append((filename, adds, removes, isbinary))
 
+    # inheader is used to track if a line is in the
+    # header portion of the diff.  This helps properly account
+    # for lines that start with '--' or '++'
+    inheader = False
+
     for line in lines:
         if line.startswith('diff'):
             addresult()
-            # set numbers to 0 anyway when starting new file
+            # starting a new file diff
+            # set numbers to 0 and reset inheader
+            inheader = True
             adds, removes, isbinary = 0, 0, False
             if line.startswith('diff --git a/'):
                 filename = gitre.search(line).group(2)
             elif line.startswith('diff -r'):
                 # format: "diff -r ... -r ... filename"
                 filename = diffre.search(line).group(1)
-        elif line.startswith('+') and not line.startswith('+++ '):
+        elif line.startswith('@@'):
+            inheader = False
+        elif line.startswith('+') and not inheader:
             adds += 1
-        elif line.startswith('-') and not line.startswith('--- '):
+        elif line.startswith('-') and not inheader:
             removes += 1
         elif (line.startswith('GIT binary patch') or
               line.startswith('Binary file')):

--- a/tests/test-diffstat.t	Fri May 19 12:38:34 2017 +0200
+++ b/tests/test-diffstat.t	Wed May 17 20:51:17 2017 -0500
@@ -105,3 +105,83 @@
   $ hg diff --stat --root . -I old
 
   $ cd ..
+
+Files with lines beginning with '--' or '++' should be properly counted in diffstat
+
+  $ hg up -Cr tip
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ rm dir1/new
+  $ rm dir2/new
+  $ rm "file with spaces"
+  $ cat > file << EOF
+  > line 1
+  > line 2
+  > line 3
+  > EOF
+  $ hg commit -Am file
+  adding file
+
+Lines added starting with '--' should count as additions
+  $ cat > file << EOF
+  > line 1
+  > -- line 2, with dashes
+  > line 3
+  > EOF
+
+  $ hg diff --root .
+  diff -r be1569354b24 file
+  --- a/file	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/file	* (glob)
+  @@ -1,3 +1,3 @@
+   line 1
+  -line 2
+  +-- line 2, with dashes
+   line 3
+
+  $ hg diff --root . --stat
+   file |  2 +-
+   1 files changed, 1 insertions(+), 1 deletions(-)
+
+Lines changed starting with '--' should count as deletions
+  $ hg commit -m filev2
+  $ cat > file << EOF
+  > line 1
+  > -- line 2, with dashes, changed again
+  > line 3
+  > EOF
+
+  $ hg diff --root .
+  diff -r 160f7c034df6 file
+  --- a/file	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/file	* (glob)
+  @@ -1,3 +1,3 @@
+   line 1
+  --- line 2, with dashes
+  +-- line 2, with dashes, changed again
+   line 3
+
+  $ hg diff --root . --stat
+   file |  2 +-
+   1 files changed, 1 insertions(+), 1 deletions(-)
+
+Lines changed starting with '--' should count as deletions
+and starting with '++' should count as additions
+  $ cat > file << EOF
+  > line 1
+  > ++ line 2, switched dashes to plusses
+  > line 3
+  > EOF
+
+  $ hg diff --root .
+  diff -r 160f7c034df6 file
+  --- a/file	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/file	* (glob)
+  @@ -1,3 +1,3 @@
+   line 1
+  --- line 2, with dashes
+  +++ line 2, switched dashes to plusses
+   line 3
+
+  $ hg diff --root . --stat
+   file |  2 +-
+   1 files changed, 1 insertions(+), 1 deletions(-)