diff --git a/src/buffer.c b/src/buffer.c
index f633c5e02..c066d8e84 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -33,7 +33,7 @@ void git_buf_init(git_buf *buf, size_t initial_size)
 }
 
 int git_buf_try_grow(
-	git_buf *buf, size_t target_size, bool mark_oom, bool preserve_external)
+	git_buf *buf, size_t target_size, bool mark_oom)
 {
 	char *new_ptr;
 	size_t new_size;
@@ -41,6 +41,9 @@ int git_buf_try_grow(
 	if (buf->ptr == git_buf__oom)
 		return -1;
 
+	if (buf->asize == 0 && buf->size != 0)
+		return GIT_EINVALIDSPEC;
+
 	if (!target_size)
 		target_size = buf->size;
 
@@ -82,9 +85,6 @@ int git_buf_try_grow(
 		return -1;
 	}
 
-	if (preserve_external && !buf->asize && buf->ptr != NULL && buf->size > 0)
-		memcpy(new_ptr, buf->ptr, min(buf->size, new_size));
-
 	buf->asize = new_size;
 	buf->ptr   = new_ptr;
 
@@ -98,7 +98,7 @@ int git_buf_try_grow(
 
 int git_buf_grow(git_buf *buffer, size_t target_size)
 {
-	return git_buf_try_grow(buffer, target_size, true, true);
+	return git_buf_try_grow(buffer, target_size, true);
 }
 
 int git_buf_grow_by(git_buf *buffer, size_t additional_size)
@@ -110,7 +110,7 @@ int git_buf_grow_by(git_buf *buffer, size_t additional_size)
 		return -1;
 	}
 
-	return git_buf_try_grow(buffer, newsize, true, true);	
+	return git_buf_try_grow(buffer, newsize, true);
 }
 
 void git_buf_free(git_buf *buf)
diff --git a/src/buffer.h b/src/buffer.h
index 093ed9b60..e46ee5dd7 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -59,7 +59,7 @@ extern int git_buf_grow_by(git_buf *buffer, size_t additional_size);
  * into the newly allocated buffer.
  */
 extern int git_buf_try_grow(
-	git_buf *buf, size_t target_size, bool mark_oom, bool preserve_external);
+	git_buf *buf, size_t target_size, bool mark_oom);
 
 /**
  * Sanitizes git_buf structures provided from user input.  Users of the
diff --git a/src/path.c b/src/path.c
index c2c90e48d..2558058dd 100644
--- a/src/path.c
+++ b/src/path.c
@@ -640,7 +640,7 @@ static bool _check_dir_contents(
 	/* leave base valid even if we could not make space for subdir */
 	if (GIT_ADD_SIZET_OVERFLOW(&alloc_size, dir_size, sub_size) ||
 		GIT_ADD_SIZET_OVERFLOW(&alloc_size, alloc_size, 2) ||
-		git_buf_try_grow(dir, alloc_size, false, false) < 0)
+		git_buf_try_grow(dir, alloc_size, false) < 0)
 		return false;
 
 	/* save excursion */
@@ -847,7 +847,7 @@ int git_path_make_relative(git_buf *path, const char *parent)
 
 	/* save the offset as we might realllocate the pointer */
 	offset = p - path->ptr;
-	if (git_buf_try_grow(path, alloclen, 1, 0) < 0)
+	if (git_buf_try_grow(path, alloclen, 1) < 0)
 		return -1;
 	p = path->ptr + offset;
 
diff --git a/tests/core/buffer.c b/tests/core/buffer.c
index fef37f8f7..cc2d7bbcc 100644
--- a/tests/core/buffer.c
+++ b/tests/core/buffer.c
@@ -1153,3 +1153,16 @@ void test_core_buffer__lf_and_crlf_conversions(void)
 	git_buf_free(&src);
 	git_buf_free(&tgt);
 }
+
+void test_core_buffer__dont_grow_borrowed(void)
+{
+	const char *somestring = "blah blah";
+	git_buf buf = GIT_BUF_INIT;
+
+	git_buf_attach_notowned(&buf, somestring, strlen(somestring) + 1);
+	cl_assert_equal_p(somestring, buf.ptr);
+	cl_assert_equal_i(0, buf.asize);
+	cl_assert_equal_i(strlen(somestring) + 1, buf.size);
+
+	cl_git_fail_with(GIT_EINVALIDSPEC, git_buf_grow(&buf, 1024));
+}