diff --git a/Documentation/RelNotes/1.8.5.6.txt b/Documentation/RelNotes/1.8.5.6.txt
new file mode 100644
index 0000000..92ff92b
--- /dev/null
+++ b/Documentation/RelNotes/1.8.5.6.txt
@@ -0,0 +1,34 @@
+Git v1.8.5.6 Release Notes
+==========================
+
+Fixes since v1.8.5.5
+--------------------
+
+ * We used to allow committing a path ".Git/config" with Git that is
+   running on a case sensitive filesystem, but an attempt to check out
+   such a path with Git that runs on a case insensitive filesystem
+   would have clobbered ".git/config", which is definitely not what
+   the user would have expected.  Git now prevents you from tracking
+   a path with ".Git" (in any case combination) as a path component.
+
+ * On Windows, certain path components that are different from ".git"
+   are mapped to ".git", e.g. "git~1/config" is treated as if it were
+   ".git/config".  HFS+ has a similar issue, where certain unicode
+   codepoints are ignored, e.g. ".g\u200cit/config" is treated as if
+   it were ".git/config".  Pathnames with these potential issues are
+   rejected on the affected systems.  Git on systems that are not
+   affected by this issue (e.g. Linux) can also be configured to
+   reject them to ensure cross platform interoperability of the hosted
+   projects.
+
+ * "git fsck" notices a tree object that records such a path that can
+   be confused with ".git", and with receive.fsckObjects configuration
+   set to true, an attempt to "git push" such a tree object will be
+   rejected.  Such a path may not be a problem on a well behaving
+   filesystem but in order to protect those on HFS+ and on case
+   insensitive filesystems, this check is enabled on all platforms.
+
+A big "thanks!" for bringing this issue to us goes to our friends in
+the Mercurial land, namely, Matt Mackall and Augie Fackler.
+
+Also contains typofixes, documentation updates and trivial code clean-ups.
diff --git a/Documentation/RelNotes/1.9.5.txt b/Documentation/RelNotes/1.9.5.txt
new file mode 100644
index 0000000..8d6ac0c
--- /dev/null
+++ b/Documentation/RelNotes/1.9.5.txt
@@ -0,0 +1,34 @@
+Git v1.9.5 Release Notes
+========================
+
+Fixes since v1.9.4
+------------------
+
+ * We used to allow committing a path ".Git/config" with Git that is
+   running on a case sensitive filesystem, but an attempt to check out
+   such a path with Git that runs on a case insensitive filesystem
+   would have clobbered ".git/config", which is definitely not what
+   the user would have expected.  Git now prevents you from tracking
+   a path with ".Git" (in any case combination) as a path component.
+
+ * On Windows, certain path components that are different from ".git"
+   are mapped to ".git", e.g. "git~1/config" is treated as if it were
+   ".git/config".  HFS+ has a similar issue, where certain unicode
+   codepoints are ignored, e.g. ".g\u200cit/config" is treated as if
+   it were ".git/config".  Pathnames with these potential issues are
+   rejected on the affected systems.  Git on systems that are not
+   affected by this issue (e.g. Linux) can also be configured to
+   reject them to ensure cross platform interoperability of the hosted
+   projects.
+
+ * "git fsck" notices a tree object that records such a path that can
+   be confused with ".git", and with receive.fsckObjects configuration
+   set to true, an attempt to "git push" such a tree object will be
+   rejected.  Such a path may not be a problem on a well behaving
+   filesystem but in order to protect those on HFS+ and on case
+   insensitive filesystems, this check is enabled on all platforms.
+
+A big "thanks!" for bringing this issue to us goes to our friends in
+the Mercurial land, namely, Matt Mackall and Augie Fackler.
+
+Also contains typofixes, documentation updates and trivial code clean-ups.
diff --git a/Documentation/RelNotes/2.0.5.txt b/Documentation/RelNotes/2.0.5.txt
new file mode 100644
index 0000000..3a16f69
--- /dev/null
+++ b/Documentation/RelNotes/2.0.5.txt
@@ -0,0 +1,34 @@
+Git v2.0.5 Release Notes
+========================
+
+Fixes since v2.0.4
+------------------
+
+ * We used to allow committing a path ".Git/config" with Git that is
+   running on a case sensitive filesystem, but an attempt to check out
+   such a path with Git that runs on a case insensitive filesystem
+   would have clobbered ".git/config", which is definitely not what
+   the user would have expected.  Git now prevents you from tracking
+   a path with ".Git" (in any case combination) as a path component.
+
+ * On Windows, certain path components that are different from ".git"
+   are mapped to ".git", e.g. "git~1/config" is treated as if it were
+   ".git/config".  HFS+ has a similar issue, where certain unicode
+   codepoints are ignored, e.g. ".g\u200cit/config" is treated as if
+   it were ".git/config".  Pathnames with these potential issues are
+   rejected on the affected systems.  Git on systems that are not
+   affected by this issue (e.g. Linux) can also be configured to
+   reject them to ensure cross platform interoperability of the hosted
+   projects.
+
+ * "git fsck" notices a tree object that records such a path that can
+   be confused with ".git", and with receive.fsckObjects configuration
+   set to true, an attempt to "git push" such a tree object will be
+   rejected.  Such a path may not be a problem on a well behaving
+   filesystem but in order to protect those on HFS+ and on case
+   insensitive filesystems, this check is enabled on all platforms.
+
+A big "thanks!" for bringing this issue to us goes to our friends in
+the Mercurial land, namely, Matt Mackall and Augie Fackler.
+
+Also contains typofixes, documentation updates and trivial code clean-ups.
diff --git a/Documentation/config.txt b/Documentation/config.txt
index 6ae4d90..0a4d22a 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -233,6 +233,17 @@
 	When false, file names are handled fully transparent by Git,
 	which is backward compatible with older versions of Git.
 
+core.protectHFS::
+	If set to true, do not allow checkout of paths that would
+	be considered equivalent to `.git` on an HFS+ filesystem.
+	Defaults to `true` on Mac OS, and `false` elsewhere.
+
+core.protectNTFS::
+	If set to true, do not allow checkout of paths that would
+	cause problems with the NTFS filesystem, e.g. conflict with
+	8.3 "short" names.
+	Defaults to `true` on Windows, and `false` elsewhere.
+
 core.trustctime::
 	If false, the ctime differences between the index and the
 	working tree are ignored; useful when the inode change time
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 5627845..ffde2b8 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -51,27 +51,30 @@
   link:RelNotes/2.1.1.txt[2.1.1],
   link:RelNotes/2.1.0.txt[2.1].
 
-* link:v2.0.4/git.html[documentation for release 2.0.4]
+* link:v2.0.5/git.html[documentation for release 2.0.5]
 
 * release notes for
+  link:RelNotes/2.0.5.txt[2.0.5],
   link:RelNotes/2.0.4.txt[2.0.4],
   link:RelNotes/2.0.3.txt[2.0.3],
   link:RelNotes/2.0.2.txt[2.0.2],
   link:RelNotes/2.0.1.txt[2.0.1],
   link:RelNotes/2.0.0.txt[2.0.0].
 
-* link:v1.9.4/git.html[documentation for release 1.9.4]
+* link:v1.9.5/git.html[documentation for release 1.9.5]
 
 * release notes for
+  link:RelNotes/1.9.5.txt[1.9.5],
   link:RelNotes/1.9.4.txt[1.9.4],
   link:RelNotes/1.9.3.txt[1.9.3],
   link:RelNotes/1.9.2.txt[1.9.2],
   link:RelNotes/1.9.1.txt[1.9.1],
   link:RelNotes/1.9.0.txt[1.9.0].
 
-* link:v1.8.5.5/git.html[documentation for release 1.8.5.5]
+* link:v1.8.5.6/git.html[documentation for release 1.8.5.6]
 
 * release notes for
+  link:RelNotes/1.8.5.6.txt[1.8.5.6],
   link:RelNotes/1.8.5.5.txt[1.8.5.5],
   link:RelNotes/1.8.5.4.txt[1.8.5.4],
   link:RelNotes/1.8.5.3.txt[1.8.5.3],
diff --git a/cache.h b/cache.h
index dcf3a2a..a258d80 100644
--- a/cache.h
+++ b/cache.h
@@ -633,6 +633,8 @@
 extern int core_preload_index;
 extern int core_apply_sparse_checkout;
 extern int precomposed_unicode;
+extern int protect_hfs;
+extern int protect_ntfs;
 
 /*
  * The character that begins a commented line in user-editable file
@@ -847,6 +849,7 @@
 int longest_ancestor_length(const char *path, struct string_list *prefixes);
 char *strip_path_suffix(const char *path, const char *suffix);
 int daemon_avoid_alias(const char *path);
+extern int is_ntfs_dotgit(const char *name);
 
 /* object replacement */
 #define LOOKUP_REPLACE_OBJECT 1
diff --git a/config.c b/config.c
index 9e42d38..73d8205 100644
--- a/config.c
+++ b/config.c
@@ -880,6 +880,16 @@
 		return 0;
 	}
 
+	if (!strcmp(var, "core.protecthfs")) {
+		protect_hfs = git_config_bool(var, value);
+		return 0;
+	}
+
+	if (!strcmp(var, "core.protectntfs")) {
+		protect_ntfs = git_config_bool(var, value);
+		return 0;
+	}
+
 	/* Add other config variables here and to Documentation/config.txt. */
 	return 0;
 }
diff --git a/config.mak.uname b/config.mak.uname
index 15ee15e..0941e30 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -100,6 +100,7 @@
 	HAVE_DEV_TTY = YesPlease
 	COMPAT_OBJS += compat/precompose_utf8.o
 	BASIC_CFLAGS += -DPRECOMPOSE_UNICODE
+	BASIC_CFLAGS += -DPROTECT_HFS_DEFAULT=1
 endif
 ifeq ($(uname_S),SunOS)
 	NEEDS_SOCKET = YesPlease
@@ -368,6 +369,7 @@
 	EXTLIBS = user32.lib advapi32.lib shell32.lib wininet.lib ws2_32.lib invalidcontinue.obj
 	PTHREAD_LIBS =
 	lib =
+	BASIC_CFLAGS += -DPROTECT_NTFS_DEFAULT=1
 ifndef DEBUG
 	BASIC_CFLAGS += -GL -Os -MD
 	BASIC_LDFLAGS += -LTCG
@@ -509,6 +511,7 @@
 	COMPAT_OBJS += compat/mingw.o compat/winansi.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
 		compat/win32/dirent.o
+	BASIC_CFLAGS += -DPROTECT_NTFS_DEFAULT=1
 	BASIC_LDFLAGS += -Wl,--large-address-aware
 	EXTLIBS += -lws2_32
 	GITLIBS += git.res
diff --git a/environment.c b/environment.c
index 565f652..1ade5c9 100644
--- a/environment.c
+++ b/environment.c
@@ -64,6 +64,16 @@
 struct startup_info *startup_info;
 unsigned long pack_size_limit_cfg;
 
+#ifndef PROTECT_HFS_DEFAULT
+#define PROTECT_HFS_DEFAULT 0
+#endif
+int protect_hfs = PROTECT_HFS_DEFAULT;
+
+#ifndef PROTECT_NTFS_DEFAULT
+#define PROTECT_NTFS_DEFAULT 0
+#endif
+int protect_ntfs = PROTECT_NTFS_DEFAULT;
+
 /*
  * The character that begins a commented line in user-editable file
  * that is subject to stripspace.
diff --git a/fsck.c b/fsck.c
index 56156ff..50c6507 100644
--- a/fsck.c
+++ b/fsck.c
@@ -6,6 +6,7 @@
 #include "commit.h"
 #include "tag.h"
 #include "fsck.h"
+#include "utf8.h"
 
 static int fsck_walk_tree(struct tree *tree, fsck_walk_func walk, void *data)
 {
@@ -170,7 +171,9 @@
 		has_empty_name |= !*name;
 		has_dot |= !strcmp(name, ".");
 		has_dotdot |= !strcmp(name, "..");
-		has_dotgit |= !strcmp(name, ".git");
+		has_dotgit |= (!strcmp(name, ".git") ||
+			       is_hfs_dotgit(name) ||
+			       is_ntfs_dotgit(name));
 		has_zero_pad |= *(char *)desc.buffer == '0';
 		update_tree_entry(&desc);
 
diff --git a/path.c b/path.c
index 3afcdb4..757d0b0 100644
--- a/path.c
+++ b/path.c
@@ -821,3 +821,36 @@
 		}
 	}
 }
+
+static int only_spaces_and_periods(const char *path, size_t len, size_t skip)
+{
+	if (len < skip)
+		return 0;
+	len -= skip;
+	path += skip;
+	while (len-- > 0) {
+		char c = *(path++);
+		if (c != ' ' && c != '.')
+			return 0;
+	}
+	return 1;
+}
+
+int is_ntfs_dotgit(const char *name)
+{
+	int len;
+
+	for (len = 0; ; len++)
+		if (!name[len] || name[len] == '\\' || is_dir_sep(name[len])) {
+			if (only_spaces_and_periods(name, len, 4) &&
+					!strncasecmp(name, ".git", 4))
+				return 1;
+			if (only_spaces_and_periods(name, len, 5) &&
+					!strncasecmp(name, "git~1", 5))
+				return 1;
+			if (name[len] != '\\')
+				return 0;
+			name += len + 1;
+			len = -1;
+		}
+}
diff --git a/read-cache.c b/read-cache.c
index 6f0057f..f042693 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -16,6 +16,7 @@
 #include "varint.h"
 #include "split-index.h"
 #include "sigchain.h"
+#include "utf8.h"
 
 static struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
 					       unsigned int options);
@@ -775,9 +776,10 @@
 	 * shares the path end test with the ".." case.
 	 */
 	case 'g':
-		if (rest[1] != 'i')
+	case 'G':
+		if (rest[1] != 'i' && rest[1] != 'I')
 			break;
-		if (rest[2] != 't')
+		if (rest[2] != 't' && rest[2] != 'T')
 			break;
 		rest += 2;
 	/* fallthrough */
@@ -801,6 +803,10 @@
 			return 1;
 		if (is_dir_sep(c)) {
 inside:
+			if (protect_hfs && is_hfs_dotgit(path))
+				return 0;
+			if (protect_ntfs && is_ntfs_dotgit(path))
+				return 0;
 			c = *path++;
 			if ((c == '.' && !verify_dotfile(path)) ||
 			    is_dir_sep(c) || c == '\0')
diff --git a/t/t1014-read-tree-confusing.sh b/t/t1014-read-tree-confusing.sh
new file mode 100755
index 0000000..2f5a25d
--- /dev/null
+++ b/t/t1014-read-tree-confusing.sh
@@ -0,0 +1,62 @@
+#!/bin/sh
+
+test_description='check that read-tree rejects confusing paths'
+. ./test-lib.sh
+
+test_expect_success 'create base tree' '
+	echo content >file &&
+	git add file &&
+	git commit -m base &&
+	blob=$(git rev-parse HEAD:file) &&
+	tree=$(git rev-parse HEAD^{tree})
+'
+
+test_expect_success 'enable core.protectHFS for rejection tests' '
+	git config core.protectHFS true
+'
+
+test_expect_success 'enable core.protectNTFS for rejection tests' '
+	git config core.protectNTFS true
+'
+
+while read path pretty; do
+	: ${pretty:=$path}
+	case "$path" in
+	*SPACE)
+		path="${path%SPACE} "
+		;;
+	esac
+	test_expect_success "reject $pretty at end of path" '
+		printf "100644 blob %s\t%s" "$blob" "$path" >tree &&
+		bogus=$(git mktree <tree) &&
+		test_must_fail git read-tree $bogus
+	'
+
+	test_expect_success "reject $pretty as subtree" '
+		printf "040000 tree %s\t%s" "$tree" "$path" >tree &&
+		bogus=$(git mktree <tree) &&
+		test_must_fail git read-tree $bogus
+	'
+done <<-EOF
+.
+..
+.git
+.GIT
+${u200c}.Git {u200c}.Git
+.gI${u200c}T .gI{u200c}T
+.GiT${u200c} .GiT{u200c}
+git~1
+.git.SPACE .git.{space}
+.\\\\.GIT\\\\foobar backslashes
+.git\\\\foobar backslashes2
+EOF
+
+test_expect_success 'utf-8 paths allowed with core.protectHFS off' '
+	test_when_finished "git read-tree HEAD" &&
+	test_config core.protectHFS false &&
+	printf "100644 blob %s\t%s" "$blob" ".gi${u200c}t" >tree &&
+	ok=$(git mktree <tree) &&
+	git read-tree $ok
+'
+
+test_done
diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index b52397a..426f753 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -271,36 +271,41 @@
 	)
 '
 
-test_expect_success 'fsck notices "." and ".." in trees' '
-	(
-		git init dots &&
-		cd dots &&
-		blob=$(echo foo | git hash-object -w --stdin) &&
-		tab=$(printf "\\t") &&
-		git mktree <<-EOF &&
-		100644 blob $blob$tab.
-		100644 blob $blob$tab..
-		EOF
-		git fsck 2>out &&
-		cat out &&
-		grep "warning.*\\." out
-	)
-'
-
-test_expect_success 'fsck notices ".git" in trees' '
-	(
-		git init dotgit &&
-		cd dotgit &&
-		blob=$(echo foo | git hash-object -w --stdin) &&
-		tab=$(printf "\\t") &&
-		git mktree <<-EOF &&
-		100644 blob $blob$tab.git
-		EOF
-		git fsck 2>out &&
-		cat out &&
-		grep "warning.*\\.git" out
-	)
-'
+while read name path pretty; do
+	while read mode type; do
+		: ${pretty:=$path}
+		test_expect_success "fsck notices $pretty as $type" '
+		(
+			git init $name-$type &&
+			cd $name-$type &&
+			echo content >file &&
+			git add file &&
+			git commit -m base &&
+			blob=$(git rev-parse :file) &&
+			tree=$(git rev-parse HEAD^{tree}) &&
+			value=$(eval "echo \$$type") &&
+			printf "$mode $type %s\t%s" "$value" "$path" >bad &&
+			bad_tree=$(git mktree <bad) &&
+			git fsck 2>out &&
+			cat out &&
+			grep "warning.*tree $bad_tree" out
+		)'
+	done <<-\EOF
+	100644 blob
+	040000 tree
+	EOF
+done <<-EOF
+dot .
+dotdot ..
+dotgit .git
+dotgit-case .GIT
+dotgit-unicode .gI${u200c}T .gI{u200c}T
+dotgit-case2 .Git
+git-tilde1 git~1
+dotgitdot .git.
+dot-backslash-case .\\\\.GIT\\\\foobar
+dotgit-case-backslash .git\\\\foobar
+EOF
 
 # create a static test repo which is broken by omitting
 # one particular object ($1, which is looked up via rev-parse
diff --git a/t/test-lib.sh b/t/test-lib.sh
index b1bc65b..a7a4639 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -169,7 +169,11 @@
 LF='
 '
 
-export _x05 _x40 _z40 LF
+# UTF-8 ZERO WIDTH NON-JOINER, which HFS+ ignores
+# when case-folding filenames
+u200c=$(printf '\342\200\214')
+
+export _x05 _x40 _z40 LF u200c
 
 # Each test should start with something like this, after copyright notices:
 #
diff --git a/unpack-trees.c b/unpack-trees.c
index 629c658..256df47 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -98,7 +98,7 @@
 		opts->unpack_rejects[i].strdup_strings = 1;
 }
 
-static void do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
+static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			 unsigned int set, unsigned int clear)
 {
 	clear |= CE_HASHED;
@@ -107,8 +107,8 @@
 		set |= CE_WT_REMOVE;
 
 	ce->ce_flags = (ce->ce_flags & ~clear) | set;
-	add_index_entry(&o->result, ce,
-			ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
+	return add_index_entry(&o->result, ce,
+			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
 static struct cache_entry *dup_entry(const struct cache_entry *ce)
@@ -609,7 +609,9 @@
 
 	for (i = 0; i < n; i++)
 		if (src[i] && src[i] != o->df_conflict_entry)
-			do_add_entry(o, src[i], 0, 0);
+			if (do_add_entry(o, src[i], 0, 0))
+				return -1;
+
 	return 0;
 }
 
diff --git a/utf8.c b/utf8.c
index b30790d..3b77e97 100644
--- a/utf8.c
+++ b/utf8.c
@@ -565,3 +565,67 @@
 
 	return chrlen;
 }
+
+/*
+ * Pick the next char from the stream, folding as an HFS+ filename comparison
+ * would. Note that this is _not_ complete by any means. It's just enough
+ * to make is_hfs_dotgit() work, and should not be used otherwise.
+ */
+static ucs_char_t next_hfs_char(const char **in)
+{
+	while (1) {
+		ucs_char_t out = pick_one_utf8_char(in, NULL);
+		/*
+		 * check for malformed utf8. Technically this
+		 * gets converted to a percent-sequence, but
+		 * returning 0 is good enough for is_hfs_dotgit
+		 * to realize it cannot be .git
+		 */
+		if (!*in)
+			return 0;
+
+		/* these code points are ignored completely */
+		switch (out) {
+		case 0x200c: /* ZERO WIDTH NON-JOINER */
+		case 0x200d: /* ZERO WIDTH JOINER */
+		case 0x200e: /* LEFT-TO-RIGHT MARK */
+		case 0x200f: /* RIGHT-TO-LEFT MARK */
+		case 0x202a: /* LEFT-TO-RIGHT EMBEDDING */
+		case 0x202b: /* RIGHT-TO-LEFT EMBEDDING */
+		case 0x202c: /* POP DIRECTIONAL FORMATTING */
+		case 0x202d: /* LEFT-TO-RIGHT OVERRIDE */
+		case 0x202e: /* RIGHT-TO-LEFT OVERRIDE */
+		case 0x206a: /* INHIBIT SYMMETRIC SWAPPING */
+		case 0x206b: /* ACTIVATE SYMMETRIC SWAPPING */
+		case 0x206c: /* INHIBIT ARABIC FORM SHAPING */
+		case 0x206d: /* ACTIVATE ARABIC FORM SHAPING */
+		case 0x206e: /* NATIONAL DIGIT SHAPES */
+		case 0x206f: /* NOMINAL DIGIT SHAPES */
+		case 0xfeff: /* ZERO WIDTH NO-BREAK SPACE */
+			continue;
+		}
+
+		/*
+		 * there's a great deal of other case-folding that occurs,
+		 * but this is enough to catch anything that will convert
+		 * to ".git"
+		 */
+		return tolower(out);
+	}
+}
+
+int is_hfs_dotgit(const char *path)
+{
+	ucs_char_t c;
+
+	if (next_hfs_char(&path) != '.' ||
+	    next_hfs_char(&path) != 'g' ||
+	    next_hfs_char(&path) != 'i' ||
+	    next_hfs_char(&path) != 't')
+		return 0;
+	c = next_hfs_char(&path);
+	if (c && !is_dir_sep(c))
+		return 0;
+
+	return 1;
+}
diff --git a/utf8.h b/utf8.h
index 65d0e42..e4d9183 100644
--- a/utf8.h
+++ b/utf8.h
@@ -42,4 +42,12 @@
 
 int mbs_chrlen(const char **text, size_t *remainder_p, const char *encoding);
 
+/*
+ * Returns true if the the path would match ".git" after HFS case-folding.
+ * The path should be NUL-terminated, but we will match variants of both ".git\0"
+ * and ".git/..." (but _not_ ".../.git"). This makes it suitable for both fsck
+ * and verify_path().
+ */
+int is_hfs_dotgit(const char *path);
+
 #endif