diff --git a/src/buffer.c b/src/buffer.c
index 27e20d562..def3496ce 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -328,6 +328,10 @@ int git_buf_join(
 	size_t strlen_a = strlen(str_a);
 	size_t strlen_b = strlen(str_b);
 	int need_sep = 0;
+	ssize_t offset_a = -1;
+
+	/* not safe to have str_b point internally to the buffer */
+	assert(str_b < buf->ptr || str_b > buf->ptr + buf->size);
 
 	/* figure out if we need to insert a separator */
 	if (separator && strlen_a) {
@@ -336,14 +340,24 @@ int git_buf_join(
 			need_sep = 1;
 	}
 
+	/* str_a could be part of the buffer */
+	if (str_a >= buf->ptr && str_a < buf->ptr + buf->size)
+		offset_a = str_a - buf->ptr;
+
 	error = git_buf_grow(buf, strlen_a + strlen_b + need_sep + 1);
 	if (error < GIT_SUCCESS)
 		return error;
 
-	memmove(buf->ptr, str_a, strlen_a);
+	/* fix up internal pointers */
+	if (offset_a >= 0)
+		str_a = buf->ptr + offset_a;
+
+	/* do the actual copying */
+	if (offset_a != 0)
+		memmove(buf->ptr, str_a, strlen_a);
 	if (need_sep)
 		buf->ptr[strlen_a] = separator;
-	memmove(buf->ptr + strlen_a + need_sep, str_b, strlen_b);
+	memcpy(buf->ptr + strlen_a + need_sep, str_b, strlen_b);
 
 	buf->size = strlen_a + strlen_b + need_sep;
 	buf->ptr[buf->size] = '\0';
diff --git a/tests-clay/clay.h b/tests-clay/clay.h
index 3f09d4f06..5db24a4c9 100644
--- a/tests-clay/clay.h
+++ b/tests-clay/clay.h
@@ -106,12 +106,13 @@ extern void test_core_filebuf__4(void);
 extern void test_core_filebuf__5(void);
 extern void test_core_oid__initialize(void);
 extern void test_core_oid__streq(void);
-extern void test_core_path__0(void);
-extern void test_core_path__1(void);
-extern void test_core_path__2(void);
-extern void test_core_path__5(void);
-extern void test_core_path__6(void);
-extern void test_core_path__7(void);
+extern void test_core_path__0_dirname(void);
+extern void test_core_path__1_basename(void);
+extern void test_core_path__2_topdir(void);
+extern void test_core_path__5_joins(void);
+extern void test_core_path__6_long_joins(void);
+extern void test_core_path__7_path_to_dir(void);
+extern void test_core_path__8_self_join(void);
 extern void test_core_rmdir__delete_recursive(void);
 extern void test_core_rmdir__fail_to_delete_non_empty_dir(void);
 extern void test_core_rmdir__initialize(void);
diff --git a/tests-clay/clay_main.c b/tests-clay/clay_main.c
index ce3b66b87..80c13f429 100644
--- a/tests-clay/clay_main.c
+++ b/tests-clay/clay_main.c
@@ -167,12 +167,13 @@ static const struct clay_func _clay_cb_core_oid[] = {
     {"streq", &test_core_oid__streq}
 };
 static const struct clay_func _clay_cb_core_path[] = {
-    {"0", &test_core_path__0},
-	{"1", &test_core_path__1},
-	{"2", &test_core_path__2},
-	{"5", &test_core_path__5},
-	{"6", &test_core_path__6},
-	{"7", &test_core_path__7}
+    {"0_dirname", &test_core_path__0_dirname},
+	{"1_basename", &test_core_path__1_basename},
+	{"2_topdir", &test_core_path__2_topdir},
+	{"5_joins", &test_core_path__5_joins},
+	{"6_long_joins", &test_core_path__6_long_joins},
+	{"7_path_to_dir", &test_core_path__7_path_to_dir},
+	{"8_self_join", &test_core_path__8_self_join}
 };
 static const struct clay_func _clay_cb_core_rmdir[] = {
     {"delete_recursive", &test_core_rmdir__delete_recursive},
@@ -361,7 +362,7 @@ static const struct clay_suite _clay_suites[] = {
         "core::path",
         {NULL, NULL},
         {NULL, NULL},
-        _clay_cb_core_path, 6
+        _clay_cb_core_path, 7
     },
 	{
         "core::rmdir",
@@ -516,7 +517,7 @@ static const struct clay_suite _clay_suites[] = {
 };
 
 static size_t _clay_suite_count = 36;
-static size_t _clay_callback_count = 119;
+static size_t _clay_callback_count = 120;
 
 /* Core test functions */
 static void
diff --git a/tests-clay/core/path.c b/tests-clay/core/path.c
index 1a588a39f..49f85f085 100644
--- a/tests-clay/core/path.c
+++ b/tests-clay/core/path.c
@@ -70,7 +70,7 @@ check_joinpath_n(
 
 
 /* get the dirname of a path */
-void test_core_path__0(void)
+void test_core_path__0_dirname(void)
 {
 	check_dirname(NULL, ".");
 	check_dirname("", ".");
@@ -90,7 +90,7 @@ void test_core_path__0(void)
 }
 
 /* get the base name of a path */
-void test_core_path__1(void)
+void test_core_path__1_basename(void)
 {
 	check_basename(NULL, ".");
 	check_basename("", ".");
@@ -107,7 +107,7 @@ void test_core_path__1(void)
 }
 
 /* get the latest component in a path */
-void test_core_path__2(void)
+void test_core_path__2_topdir(void)
 {
 	check_topdir(".git/", ".git/");
 	check_topdir("/.git/", ".git/");
@@ -124,7 +124,7 @@ void test_core_path__2(void)
 }
 
 /* properly join path components */
-void test_core_path__5(void)
+void test_core_path__5_joins(void)
 {
 	check_joinpath("", "", "");
 	check_joinpath("", "a", "a");
@@ -148,6 +148,10 @@ void test_core_path__5(void)
 	check_joinpath("/abcdefgh", "/12345678/", "/abcdefgh/12345678/");
 	check_joinpath("/abcdefgh/", "12345678/", "/abcdefgh/12345678/");
 
+	check_joinpath(REP1024("aaaa"), "", REP1024("aaaa") "/");
+	check_joinpath(REP1024("aaaa/"), "", REP1024("aaaa/"));
+	check_joinpath(REP1024("/aaaa"), "", REP1024("/aaaa") "/");
+
 	check_joinpath(REP1024("aaaa"), REP1024("bbbb"),
 				   REP1024("aaaa") "/" REP1024("bbbb"));
 	check_joinpath(REP1024("/aaaa"), REP1024("/bbbb"),
@@ -155,7 +159,7 @@ void test_core_path__5(void)
 }
 
 /* properly join path components for more than one path */
-void test_core_path__6(void)
+void test_core_path__6_long_joins(void)
 {
 	check_joinpath_n("", "", "", "", "");
 	check_joinpath_n("", "a", "", "", "a/");
@@ -208,7 +212,7 @@ check_string_to_dir(
 }
 
 /* convert paths to dirs */
-void test_core_path__7(void)
+void test_core_path__7_path_to_dir(void)
 {
 	check_path_to_dir("", "");
 	check_path_to_dir(".", "./");
@@ -234,3 +238,38 @@ void test_core_path__7(void)
 	check_string_to_dir("abcd", 5, "abcd/");
 	check_string_to_dir("abcd", 6, "abcd/");
 }
+
+/* join path to itself */
+void test_core_path__8_self_join(void)
+{
+	git_buf path = GIT_BUF_INIT;
+	ssize_t asize = 0;
+
+	asize = path.asize;
+	cl_git_pass(git_buf_sets(&path, "/foo"));
+	cl_assert_strequal(path.ptr, "/foo");
+	cl_assert(asize < path.asize);
+
+	asize = path.asize;
+	cl_git_pass(git_buf_joinpath(&path, path.ptr, "this is a new string"));
+	cl_assert_strequal(path.ptr, "/foo/this is a new string");
+	cl_assert(asize < path.asize);
+
+	asize = path.asize;
+	cl_git_pass(git_buf_joinpath(&path, path.ptr, "/grow the buffer, grow the buffer, grow the buffer"));
+	cl_assert_strequal(path.ptr, "/foo/this is a new string/grow the buffer, grow the buffer, grow the buffer");
+	cl_assert(asize < path.asize);
+
+	git_buf_free(&path);
+	cl_git_pass(git_buf_sets(&path, "/foo/bar"));
+
+	cl_git_pass(git_buf_joinpath(&path, path.ptr + 4, "baz"));
+	cl_assert_strequal(path.ptr, "/bar/baz");
+
+	asize = path.asize;
+	cl_git_pass(git_buf_joinpath(&path, path.ptr + 4, "somethinglongenoughtorealloc"));
+	cl_assert_strequal(path.ptr, "/baz/somethinglongenoughtorealloc");
+	cl_assert(asize < path.asize);
+	
+	git_buf_free(&path);
+}
diff --git a/tests/test_helpers.c b/tests/test_helpers.c
index d4ed10d94..40b3499bb 100644
--- a/tests/test_helpers.c
+++ b/tests/test_helpers.c
@@ -236,7 +236,7 @@ static int copy_filesystem_element_recurs(void *_data, git_buf *source)
 	copydir_data *data = (copydir_data *)_data;
 
 	git_buf_truncate(&data->dst, data->dst_baselen);
-	git_buf_joinpath(&data->dst, data->dst.ptr, source->ptr + data->src_baselen);
+	git_buf_puts(&data->dst, source->ptr + data->src_baselen);
 
 	if (git_futils_isdir(source->ptr) == GIT_SUCCESS)
 		return git_futils_direach(source, copy_filesystem_element_recurs, _data);