diff --git a/include/git2/errors.h b/include/git2/errors.h
index a81aa05d9..e189e55f1 100644
--- a/include/git2/errors.h
+++ b/include/git2/errors.h
@@ -48,6 +48,7 @@ typedef enum {
 	GIT_EEOF            = -20,      /**< Unexpected EOF */
 	GIT_EINVALID        = -21,      /**< Invalid operation or input */
 	GIT_EUNCOMMITTED    = -22,	/**< Uncommitted changes in index prevented operation */
+	GIT_EDIRECTORY      = -23,      /**< The operation is not valid for a directory */
 
 	GIT_PASSTHROUGH     = -30,	/**< Internal only */
 	GIT_ITEROVER        = -31,	/**< Signals end of iteration with iterator */
diff --git a/src/blob.c b/src/blob.c
index 07c4d92c8..ad0f4ac62 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -185,6 +185,12 @@ int git_blob__create_from_paths(
 		(error = git_repository_odb(&odb, repo)) < 0)
 		goto done;
 
+	if (S_ISDIR(st.st_mode)) {
+		giterr_set(GITERR_ODB, "cannot create blob from '%s'; it is a directory", content_path);
+		error = GIT_EDIRECTORY;
+		goto done;
+	}
+
 	if (out_st)
 		memcpy(out_st, &st, sizeof(st));
 
diff --git a/src/index.c b/src/index.c
index 5ce5522f8..501498e9e 100644
--- a/src/index.c
+++ b/src/index.c
@@ -1236,10 +1236,30 @@ int git_index_add_bypath(git_index *index, const char *path)
 
 	assert(index && path);
 
-	if ((ret = index_entry_init(&entry, index, path)) < 0 ||
-		(ret = index_insert(index, &entry, 1, false)) < 0)
+	if ((ret = index_entry_init(&entry, index, path)) == 0)
+		ret = index_insert(index, &entry, 1, false);
+
+	/* If we were given a directory, let's see if it's a submodule */
+	if (ret < 0 && ret != GIT_EDIRECTORY)
 		return ret;
 
+	if (ret == GIT_EDIRECTORY) {
+		git_submodule *sm;
+		git_error_state err;
+
+		giterr_capture(&err, ret);
+
+		ret = git_submodule_lookup(&sm, INDEX_OWNER(index), path);
+		if (ret == GIT_ENOTFOUND)
+			return giterr_restore(&err);
+		else
+			git__free(err.error_msg.message);
+
+		ret = git_submodule_add_to_index(sm, false);
+		git_submodule_free(sm);
+		return ret;
+	}
+
 	/* Adding implies conflict was resolved, move conflict entries to REUC */
 	if ((ret = index_conflict_to_reuc(index, path)) < 0 && ret != GIT_ENOTFOUND)
 		return ret;
diff --git a/tests/index/bypath.c b/tests/index/bypath.c
new file mode 100644
index 000000000..ddb766a22
--- /dev/null
+++ b/tests/index/bypath.c
@@ -0,0 +1,35 @@
+#include "clar_libgit2.h"
+#include "repository.h"
+#include "../submodule/submodule_helpers.h"
+
+static git_repository *g_repo;
+static git_index *g_idx;
+
+void test_index_bypath__initialize(void)
+{
+	g_repo = setup_fixture_submod2();
+	cl_git_pass(git_repository_index__weakptr(&g_idx, g_repo));
+}
+
+void test_index_bypath__cleanup(void)
+{
+	g_repo = NULL;
+	g_idx = NULL;
+}
+
+void test_index_bypath__add_directory(void)
+{
+	cl_git_fail_with(GIT_EDIRECTORY, git_index_add_bypath(g_idx, "just_a_dir"));
+}
+
+void test_index_bypath__add_submodule(void)
+{
+	unsigned int status;
+	const char *sm_name = "sm_changed_head";
+
+	cl_git_pass(git_submodule_status(&status, g_repo, sm_name, 0));
+	cl_assert_equal_i(GIT_SUBMODULE_STATUS_WD_MODIFIED, status & GIT_SUBMODULE_STATUS_WD_MODIFIED);
+	cl_git_pass(git_index_add_bypath(g_idx, sm_name));
+	cl_git_pass(git_submodule_status(&status, g_repo, sm_name, 0));
+	cl_assert_equal_i(0, status & GIT_SUBMODULE_STATUS_WD_MODIFIED);
+}
diff --git a/tests/submodule/add.c b/tests/submodule/add.c
index 01625d3aa..c3b3e6364 100644
--- a/tests/submodule/add.c
+++ b/tests/submodule/add.c
@@ -4,6 +4,7 @@
 #include "submodule_helpers.h"
 #include "config/config_helpers.h"
 #include "fileops.h"
+#include "repository.h"
 
 static git_repository *g_repo = NULL;