diff --git a/include/git2/gitup_index.h b/include/git2/gitup_index.h
new file mode 100644
index 00000000000..ee4fb65598b
--- /dev/null
+++ b/include/git2/gitup_index.h
@@ -0,0 +1,29 @@
+#include "common.h"
+#include "indexer.h"
+#include "types.h"
+#include "oid.h"
+#include "strarray.h"
+
+/**
+ * @file git2/index.h
+ * @brief Index (aka "cache" aka "staging area")
+ * @defgroup git_index Git index parsing and manipulation routines
+ * @ingroup Git
+ * @{
+ */
+GIT_BEGIN_DECL
+
+/**
+ * Forget the file associated with this index.
+ *
+ * This will prevent using operations that read
+ * or write to the index's on-disk file.
+ * This (probably) effectively makes this index
+ * indistinguishable from an in-memory index.
+ *
+ * @param index An index object
+ */
+GIT_EXTERN(void) git_index_forget_file(git_index *index);
+
+/** @} */
+GIT_END_DECL
diff --git a/src/libgit2/index.c b/src/libgit2/index.c
index a3142c8bcd9..868deba59e6 100644
--- a/src/libgit2/index.c
+++ b/src/libgit2/index.c
@@ -3938,6 +3938,12 @@ void git_indexwriter_cleanup(git_indexwriter *writer)
 	writer->index = NULL;
 }
 
+void git_index_forget_file(git_index *index)
+{
+	index->index_file_path = NULL;
+	index->on_disk = 0;
+}
+
 /* Deprecated functions */
 
 #ifndef GIT_DEPRECATE_HARD