diff --git a/mercurial/patch.py b/mercurial/patch.py
--- a/mercurial/patch.py
+++ b/mercurial/patch.py
@@ -47,6 +47,9 @@ def split(stream):
         if inheader and line[0] in (' ', '\t'):
             # continuation
             return True
+        if line[0] in (' ', '-', '+'):
+            # diff line - don't check for header pattern in there
+            return False
         l = line.split(': ', 1)
         return len(l) == 2 and ' ' not in l[0]
 
diff --git a/tests/test-import b/tests/test-import
--- a/tests/test-import
+++ b/tests/test-import
@@ -474,3 +474,24 @@ EOF
 hg sum
 hg diff --git -c tip
 cd ..
+
+echo '% diff lines looking like headers'
+hg init difflineslikeheaders
+cd difflineslikeheaders
+echo a >a
+echo b >b
+echo c >c
+hg ci -Am1
+
+echo "key: value" >>a
+echo "key: value" >>b
+echo "foo" >>c
+hg ci -m2
+
+hg up -C 0
+hg diff --git -c1 >want
+hg diff -c1 | hg import --no-commit -
+hg diff --git >have
+diff want have
+cd ..
+
diff --git a/tests/test-import.out b/tests/test-import.out
--- a/tests/test-import.out
+++ b/tests/test-import.out
@@ -373,3 +373,9 @@ new file mode 100644
 diff --git a/src/cmd/gc/mksys.bash b/src/cmd/gc/mksys.bash
 old mode 100644
 new mode 100755
+% diff lines looking like headers
+adding a
+adding b
+adding c
+3 files updated, 0 files merged, 0 files removed, 0 files unresolved
+applying patch from stdin