diff --git a/src/index.c b/src/index.c
index 3b8447c..c62e5f2 100644
--- a/src/index.c
+++ b/src/index.c
@@ -352,10 +352,10 @@ Index_read_tree(Index *self, PyObject *value)
     git_oid oid;
     git_tree *tree;
     int err;
-    Py_ssize_t len;
+    size_t len;
 
-    len = py_str_to_git_oid(value, &oid);
-    if (len < 0)
+    len = py_oid_to_git_oid(value, &oid);
+    if (len == 0)
         return NULL;
 
     err = git_tree_lookup_prefix(&tree, self->repo->repo, &oid, len);
diff --git a/src/oid.c b/src/oid.c
index d1751ce..f96fd1e 100644
--- a/src/oid.c
+++ b/src/oid.c
@@ -45,8 +45,8 @@ git_oid_to_python(const git_oid *oid)
     return (PyObject*)py_oid;
 }
 
-Py_ssize_t
-_oid_from_hex(PyObject *py_oid, git_oid *oid)
+size_t
+py_hex_to_git_oid (PyObject *py_oid, git_oid *oid)
 {
     PyObject *py_hex;
     int err;
@@ -58,15 +58,15 @@ _oid_from_hex(PyObject *py_oid, git_oid *oid)
     if (PyBytes_Check(py_oid)) {
         err = PyBytes_AsStringAndSize(py_oid, &hex, &len);
         if (err)
-            return -1;
+            return 0;
 
         err = git_oid_fromstrn(oid, hex, len);
         if (err < 0) {
             PyErr_SetObject(Error_type(err), py_oid);
-            return -1;
+            return 0;
         }
 
-        return len;
+        return (size_t)len;
     }
 #endif
 
@@ -74,31 +74,31 @@ _oid_from_hex(PyObject *py_oid, git_oid *oid)
     if (PyUnicode_Check(py_oid)) {
         py_hex = PyUnicode_AsASCIIString(py_oid);
         if (py_hex == NULL)
-            return -1;
+            return 0;
 
         err = PyBytes_AsStringAndSize(py_hex, &hex, &len);
         if (err) {
             Py_DECREF(py_hex);
-            return -1;
+            return 0;
         }
 
         err = git_oid_fromstrn(oid, hex, len);
         Py_DECREF(py_hex);
         if (err < 0) {
             PyErr_SetObject(Error_type(err), py_oid);
-            return -1;
+            return 0;
         }
 
-        return len;
+        return (size_t)len;
     }
 
     /* Type error */
     PyErr_SetObject(PyExc_TypeError, py_oid);
-    return -1;
+    return 0;
 }
 
-Py_ssize_t
-py_str_to_git_oid(PyObject *py_oid, git_oid *oid)
+size_t
+py_oid_to_git_oid(PyObject *py_oid, git_oid *oid)
 {
     /* Oid */
     if (PyObject_TypeCheck(py_oid, (PyTypeObject*)&OidType)) {
@@ -107,41 +107,43 @@ py_str_to_git_oid(PyObject *py_oid, git_oid *oid)
     }
 
     /* Hex */
-    return _oid_from_hex(py_oid, oid);
+    return py_hex_to_git_oid(py_oid, oid);
 }
 
-Py_ssize_t
-py_str_to_git_oid_expand(git_repository *repo, PyObject *py_str, git_oid *oid)
+int
+py_oid_to_git_oid_expand(git_repository *repo, PyObject *py_str, git_oid *oid)
 {
     int err;
-    Py_ssize_t len;
-    git_odb *odb;
-    git_odb_object *obj;
+    size_t len;
+    git_odb *odb = NULL;
+    git_odb_object *obj = NULL;
 
-    len = py_str_to_git_oid(py_str, oid);
-
-    if (len == GIT_OID_HEXSZ || len < 0)
-        return len;
-
-    err = git_repository_odb(&odb, repo);
-    if (err < 0) {
-        Error_set(err);
+    len = py_oid_to_git_oid(py_str, oid);
+    if (len == 0)
         return -1;
-    }
+
+    if (len == GIT_OID_HEXSZ)
+        return 0;
+
+    /* Short oid */
+    err = git_repository_odb(&odb, repo);
+    if (err < 0)
+        goto error;
 
     err = git_odb_read_prefix(&obj, odb, oid, len);
-    if (err < 0) {
-        git_odb_free(odb);
-        Error_set(err);
-        return err;
-    }
+    if (err < 0)
+        goto error;
 
     git_oid_cpy(oid, git_odb_object_id(obj));
-
     git_odb_object_free(obj);
     git_odb_free(odb);
-
     return 0;
+
+error:
+    git_odb_object_free(obj);
+    git_odb_free(odb);
+    Error_set(err);
+    return -1;
 }
 
 PyObject *
@@ -197,8 +199,8 @@ Oid_init(Oid *self, PyObject *args, PyObject *kw)
     }
 
     /* Case 2: hex */
-    len = _oid_from_hex(hex, &self->oid);
-    if (len < 0)
+    len = py_hex_to_git_oid(hex, &self->oid);
+    if (len == 0)
         return -1;
 
     return 0;
diff --git a/src/oid.h b/src/oid.h
index ca6567c..871f26a 100644
--- a/src/oid.h
+++ b/src/oid.h
@@ -32,9 +32,9 @@
 #include <Python.h>
 #include <git2.h>
 
-Py_ssize_t py_str_to_git_oid(PyObject *py_str, git_oid *oid);
-Py_ssize_t py_str_to_git_oid_expand(git_repository *repo, PyObject *py_str,
-                                    git_oid *oid);
+size_t py_oid_to_git_oid(PyObject *py_str, git_oid *oid);
+int py_oid_to_git_oid_expand(git_repository *repo, PyObject *py_str,
+                             git_oid *oid);
 PyObject* git_oid_to_python(const git_oid *oid);
 PyObject* git_oid_to_py_str(const git_oid *oid);
 
diff --git a/src/reference.c b/src/reference.c
index 17537e7..1e302c7 100644
--- a/src/reference.c
+++ b/src/reference.c
@@ -226,7 +226,6 @@ Reference_target__set__(Reference *self, PyObject *py_target)
     git_oid oid;
     char *c_name;
     int err;
-    Py_ssize_t len;
     git_reference *new_ref;
     git_repository *repo;
 
@@ -235,11 +234,9 @@ Reference_target__set__(Reference *self, PyObject *py_target)
     /* Case 1: Direct */
     if (GIT_REF_OID == git_reference_type(self->reference)) {
         repo = git_reference_owner(self->reference);
-        len = py_str_to_git_oid_expand(repo, py_target, &oid);
-        if (len < 0) {
-            err = (int)len;
-            goto error;
-        }
+        err = py_oid_to_git_oid_expand(repo, py_target, &oid);
+        if (err < 0)
+            return err;
 
         err = git_reference_set_target(&new_ref, self->reference, &oid);
         if (err < 0)
diff --git a/src/repository.c b/src/repository.c
index 3468ffc..0cc7c3b 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -254,12 +254,12 @@ PyObject *
 Repository_git_object_lookup_prefix(Repository *self, PyObject *key)
 {
     int err;
-    Py_ssize_t len;
+    size_t len;
     git_oid oid;
     git_object *obj;
 
-    len = py_str_to_git_oid(key, &oid);
-    if (len < 0)
+    len = py_oid_to_git_oid(key, &oid);
+    if (len == 0)
         return NULL;
 
     err = git_object_lookup_prefix(&obj, self->repo, &oid, len, GIT_OBJ_ANY);
@@ -339,11 +339,11 @@ Repository_read(Repository *self, PyObject *py_hex)
 {
     git_oid oid;
     git_odb_object *obj;
-    Py_ssize_t len;
+    size_t len;
     PyObject* tuple;
 
-    len = py_str_to_git_oid(py_hex, &oid);
-    if (len < 0)
+    len = py_oid_to_git_oid(py_hex, &oid);
+    if (len == 0)
         return NULL;
 
     obj = Repository_read_raw(self->repo, &oid, len);
@@ -522,11 +522,11 @@ Repository_merge_base(Repository *self, PyObject *args)
     if (!PyArg_ParseTuple(args, "OO", &value1, &value2))
         return NULL;
 
-    err = py_str_to_git_oid_expand(self->repo, value1, &oid1);
+    err = py_oid_to_git_oid_expand(self->repo, value1, &oid1);
     if (err < 0)
         return NULL;
 
-    err = py_str_to_git_oid_expand(self->repo, value2, &oid2);
+    err = py_oid_to_git_oid_expand(self->repo, value2, &oid2);
     if (err < 0)
         return NULL;
 
@@ -548,7 +548,6 @@ Repository_walk(Repository *self, PyObject *args)
     PyObject *value;
     unsigned int sort;
     int err;
-    Py_ssize_t len;
     git_oid oid;
     git_revwalk *walk;
     Walker *py_walker;
@@ -565,10 +564,10 @@ Repository_walk(Repository *self, PyObject *args)
 
     /* Push */
     if (value != Py_None) {
-        len = py_str_to_git_oid_expand(self->repo, value, &oid);
-        if (len < 0) {
+        err = py_oid_to_git_oid_expand(self->repo, value, &oid);
+        if (err < 0) {
             git_revwalk_free(walk);
-            return Error_set((int)len);
+            return NULL;
         }
 
         err = git_revwalk_push(walk, &oid);
@@ -683,7 +682,7 @@ Repository_create_commit(Repository *self, PyObject *args)
     int parent_count;
     git_commit **parents = NULL;
     int err = 0, i = 0;
-    Py_ssize_t len;
+    size_t len;
 
     if (!PyArg_ParseTuple(args, "zO!O!OOO!|s",
                           &update_ref,
@@ -695,8 +694,8 @@ Repository_create_commit(Repository *self, PyObject *args)
                           &encoding))
         return NULL;
 
-    len = py_str_to_git_oid(py_oid, &oid);
-    if (len < 0)
+    len = py_oid_to_git_oid(py_oid, &oid);
+    if (len == 0)
         goto out;
 
     message = py_str_to_c_str(py_message, encoding);
@@ -717,12 +716,14 @@ Repository_create_commit(Repository *self, PyObject *args)
     }
     for (; i < parent_count; i++) {
         py_parent = PyList_GET_ITEM(py_parents, i);
-        len = py_str_to_git_oid(py_parent, &oid);
-        if (len < 0)
+        len = py_oid_to_git_oid(py_parent, &oid);
+        if (len == 0)
             goto out;
-        if (git_commit_lookup_prefix(&parents[i], self->repo, &oid,
-                                     (unsigned int)len))
+        err = git_commit_lookup_prefix(&parents[i], self->repo, &oid, len);
+        if (err < 0) {
+            Error_set(err);
             goto out;
+        }
     }
 
     err = git_commit_create(&oid, self->repo, update_ref,
@@ -762,7 +763,7 @@ Repository_create_tag(Repository *self, PyObject *args)
     git_oid oid;
     git_object *target = NULL;
     int err, target_type;
-    Py_ssize_t len;
+    size_t len;
 
     if (!PyArg_ParseTuple(args, "sOiO!s",
                           &tag_name,
@@ -772,12 +773,12 @@ Repository_create_tag(Repository *self, PyObject *args)
                           &message))
         return NULL;
 
-    len = py_str_to_git_oid(py_oid, &oid);
-    if (len < 0)
+    len = py_oid_to_git_oid(py_oid, &oid);
+    if (len == 0)
         return NULL;
 
-    err = git_object_lookup_prefix(&target, self->repo, &oid,
-                                   (unsigned int)len, target_type);
+    err = git_object_lookup_prefix(&target, self->repo, &oid, len,
+                                   target_type);
     err = err < 0 ? err : git_tag_create(&oid, self->repo, tag_name, target,
                          py_tagger->signature, message, 0);
     git_object_free(target);
@@ -885,14 +886,13 @@ Repository_create_reference_direct(Repository *self,  PyObject *args,
     char *c_name;
     git_oid oid;
     int err, force;
-    Py_ssize_t len;
 
     if (!PyArg_ParseTuple(args, "sOi", &c_name, &py_obj, &force))
         return NULL;
 
-    len = py_str_to_git_oid_expand(self->repo, py_obj, &oid);
-    if (len < 0)
-        return Error_set((int)len);
+    err = py_oid_to_git_oid_expand(self->repo, py_obj, &oid);
+    if (err < 0)
+        return NULL;
 
     err = git_reference_create(&c_reference, self->repo, c_name, &oid, force);
     if (err < 0)
@@ -1013,7 +1013,6 @@ Repository_TreeBuilder(Repository *self, PyObject *args)
     git_tree *tree = NULL;
     git_tree *must_free = NULL;
     int err;
-    Py_ssize_t len;
 
     if (!PyArg_ParseTuple(args, "|O", &py_src))
         return NULL;
@@ -1027,8 +1026,8 @@ Repository_TreeBuilder(Repository *self, PyObject *args)
             }
             tree = py_tree->tree;
         } else {
-            len = py_str_to_git_oid_expand(self->repo, py_src, &oid);
-            if (len < 0)
+            err = py_oid_to_git_oid_expand(self->repo, py_src, &oid);
+            if (err < 0)
                 return NULL;
 
             err = git_tree_lookup(&tree, self->repo, &oid);
diff --git a/src/treebuilder.c b/src/treebuilder.c
index 8f52596..1724f14 100644
--- a/src/treebuilder.c
+++ b/src/treebuilder.c
@@ -53,7 +53,7 @@ PyObject *
 TreeBuilder_insert(TreeBuilder *self, PyObject *args)
 {
     PyObject *py_oid;
-    Py_ssize_t len;
+    size_t len;
     int err, attr;
     git_oid oid;
     const char *fname;
@@ -61,8 +61,8 @@ TreeBuilder_insert(TreeBuilder *self, PyObject *args)
     if (!PyArg_ParseTuple(args, "sOi", &fname, &py_oid, &attr))
         return NULL;
 
-    len = py_str_to_git_oid(py_oid, &oid);
-    if (len < 0)
+    len = py_oid_to_git_oid(py_oid, &oid);
+    if (len == 0)
         return NULL;
 
     err = git_treebuilder_insert(NULL, self->bld, fname, &oid, attr);
diff --git a/src/walker.c b/src/walker.c
index 1952fbe..a02b2f4 100644
--- a/src/walker.c
+++ b/src/walker.c
@@ -53,12 +53,11 @@ PyObject *
 Walker_hide(Walker *self, PyObject *py_hex)
 {
     int err;
-    Py_ssize_t len;
     git_oid oid;
 
-    len = py_str_to_git_oid_expand(self->repo->repo, py_hex, &oid);
-    if (len < 0)
-        return Error_set((int)len);
+    err = py_oid_to_git_oid_expand(self->repo->repo, py_hex, &oid);
+    if (err < 0)
+        return NULL;
 
     err = git_revwalk_hide(self->walk, &oid);
     if (err < 0)
@@ -77,12 +76,11 @@ PyObject *
 Walker_push(Walker *self, PyObject *py_hex)
 {
     int err;
-    Py_ssize_t len;
     git_oid oid;
 
-    len = py_str_to_git_oid_expand(self->repo->repo, py_hex, &oid);
-    if (len < 0)
-        return Error_set((int)len);
+    err = py_oid_to_git_oid_expand(self->repo->repo, py_hex, &oid);
+    if (err < 0)
+        return NULL;
 
     err = git_revwalk_push(self->walk, &oid);
     if (err < 0)