diff --git a/src/pyconstraint.c b/src/pyconstraint.c
index 7845eab..8a8ce0a 100644
--- a/src/pyconstraint.c
+++ b/src/pyconstraint.c
@@ -95,25 +95,25 @@ PyObject *_ped_Constraint_richcompare(_ped_Constraint *a, PyObject *b, int op) {
 
 PyObject *_ped_Constraint_str(_ped_Constraint *self) {
     char *ret = NULL;
-    char *start_align = NULL, *end_align = NULL;
-    char *start_range = NULL, *end_range = NULL;
+    const char *start_align = NULL, *end_align = NULL;
+    const char *start_range = NULL, *end_range = NULL;
 
-    start_align = (char *) PyUnicode_AsUTF8(_ped_Alignment_Type_obj.tp_repr(self->start_align));
+    start_align = PyUnicode_AsUTF8(_ped_Alignment_Type_obj.tp_repr(self->start_align));
     if (start_align == NULL) {
         return NULL;
     }
 
-    end_align = (char *) PyUnicode_AsUTF8(_ped_Alignment_Type_obj.tp_repr(self->end_align));
+    end_align = PyUnicode_AsUTF8(_ped_Alignment_Type_obj.tp_repr(self->end_align));
     if (end_align == NULL) {
         return NULL;
     }
 
-    start_range = (char *) PyUnicode_AsUTF8(_ped_Geometry_Type_obj.tp_repr(self->start_range));
+    start_range = PyUnicode_AsUTF8(_ped_Geometry_Type_obj.tp_repr(self->start_range));
     if (start_range == NULL) {
         return NULL;
     }
 
-    end_range = (char *) PyUnicode_AsUTF8(_ped_Geometry_Type_obj.tp_repr(self->end_range));
+    end_range = PyUnicode_AsUTF8(_ped_Geometry_Type_obj.tp_repr(self->end_range));
     if (end_range == NULL) {
         return NULL;
     }
diff --git a/src/pydevice.c b/src/pydevice.c
index 20f492e..6c09d08 100644
--- a/src/pydevice.c
+++ b/src/pydevice.c
@@ -186,14 +186,14 @@ PyObject *_ped_Device_richcompare(_ped_Device *a, PyObject *b, int op) {
 
 PyObject *_ped_Device_str(_ped_Device *self) {
     char *ret = NULL;
-    char *hw_geom = NULL, *bios_geom = NULL;
+    const char *hw_geom = NULL, *bios_geom = NULL;
 
-    hw_geom = (char *) PyUnicode_AsUTF8(_ped_CHSGeometry_Type_obj.tp_repr(self->hw_geom));
+    hw_geom = PyUnicode_AsUTF8(_ped_CHSGeometry_Type_obj.tp_repr(self->hw_geom));
     if (hw_geom == NULL) {
         return NULL;
     }
 
-    bios_geom = (char *) PyUnicode_AsUTF8(_ped_CHSGeometry_Type_obj.tp_repr(self->bios_geom));
+    bios_geom = PyUnicode_AsUTF8(_ped_CHSGeometry_Type_obj.tp_repr(self->bios_geom));
     if (bios_geom == NULL) {
         return NULL;
     }
diff --git a/src/pydisk.c b/src/pydisk.c
index 0b21141..49c5184 100644
--- a/src/pydisk.c
+++ b/src/pydisk.c
@@ -98,7 +98,7 @@ PyObject *_ped_Partition_richcompare(_ped_Partition *a, PyObject *b, int op) {
 
 PyObject *_ped_Partition_str(_ped_Partition *self) {
     char *ret = NULL;
-    char *disk = NULL, *fs_type = NULL, *geom = NULL;
+    const char *disk = NULL, *fs_type = NULL, *geom = NULL;
 
     disk = (char *) PyUnicode_AsUTF8(_ped_Disk_Type_obj.tp_repr(self->disk));
     if (disk == NULL) {
@@ -346,7 +346,7 @@ PyObject *_ped_Disk_richcompare(_ped_Disk *a, PyObject *b, int op) {
 
 PyObject *_ped_Disk_str(_ped_Disk *self) {
     char *ret = NULL;
-    char *dev = NULL, *type = NULL;
+    const char *dev = NULL, *type = NULL;
 
     dev = (char *) PyUnicode_AsUTF8(_ped_Device_Type_obj.tp_repr(self->dev));
     if (dev == NULL) {
diff --git a/src/pyfilesys.c b/src/pyfilesys.c
index 53abd90..637a61d 100644
--- a/src/pyfilesys.c
+++ b/src/pyfilesys.c
@@ -171,14 +171,14 @@ PyObject *_ped_FileSystem_richcompare(_ped_FileSystem *a, PyObject *b, int op) {
 
 PyObject *_ped_FileSystem_str(_ped_FileSystem *self) {
     char *ret = NULL;
-    char *type = NULL, *geom = NULL;
+    const char *type = NULL, *geom = NULL;
 
-    type = (char *) PyUnicode_AsUTF8(_ped_FileSystem_Type_obj.tp_repr(self->type));
+    type = PyUnicode_AsUTF8(_ped_FileSystem_Type_obj.tp_repr(self->type));
     if (type == NULL) {
         return NULL;
     }
 
-    geom = (char *) PyUnicode_AsUTF8(_ped_Geometry_Type_obj.tp_repr(self->geom));
+    geom = PyUnicode_AsUTF8(_ped_Geometry_Type_obj.tp_repr(self->geom));
     if (geom == NULL) {
         return NULL;
     }
diff --git a/src/pygeom.c b/src/pygeom.c
index 811e6f5..a4263c0 100644
--- a/src/pygeom.c
+++ b/src/pygeom.c
@@ -86,9 +86,9 @@ PyObject *_ped_Geometry_richcompare(_ped_Geometry *a, PyObject *b, int op) {
 
 PyObject *_ped_Geometry_str(_ped_Geometry *self) {
     char *ret = NULL;
-    char *dev = NULL;
+    const char *dev = NULL;
 
-    dev = (char *) PyUnicode_AsUTF8(_ped_Device_Type_obj.tp_repr(self->dev));
+    dev = PyUnicode_AsUTF8(_ped_Device_Type_obj.tp_repr(self->dev));
     if (dev == NULL) {
         return NULL;
     }
diff --git a/src/pytimer.c b/src/pytimer.c
index e3e9863..4f7f325 100644
--- a/src/pytimer.c
+++ b/src/pytimer.c
@@ -188,19 +188,21 @@ int _ped_Timer_set(_ped_Timer *self, PyObject *value, void *closure) {
             return -1;
         }
     } else if (!strcmp(member, "state_name")) {
-        self->state_name = (char *) PyUnicode_AsUTF8(value);
+        const char *state_name = PyUnicode_AsUTF8(value);
         if (PyErr_Occurred()) {
             return -1;
         }
         /* self->state_name now points to the internal buffer of a PyUnicode obj
          * which may be freed when its refcount drops to zero, so strdup it.
          */
-        if (self->state_name) {
-            self->state_name = strdup(self->state_name);
+        if (state_name) {
+            self->state_name = strdup(state_name);
             if (!self->state_name) {
                 PyErr_NoMemory();
                 return -2;
             }
+        } else {
+            self->state_name = NULL;
         }
     } else {
         PyErr_Format(PyExc_AttributeError, "_ped.Timer object has no attribute %s", member);