diff --git a/src/blob.c b/src/blob.c
index 3112132..2d5a649 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -208,12 +208,17 @@ PyObject* pysqlite_blob_write(pysqlite_Blob *self, PyObject *data)
         return NULL;
     }
 
-    if (!pysqlite_check_blob(self)) {
+    if (data_buffer.len > self->length - self->offset) {
+        PyErr_SetString(PyExc_ValueError,
+                        "data longer than blob length");
         PyBuffer_Release(&data_buffer);
         return NULL;
     }
 
-    /* TODO: throw better error on data bigger then blob. */
+    if (!pysqlite_check_blob(self)) {
+        PyBuffer_Release(&data_buffer);
+        return NULL;
+    }
 
     rc = write_inner(self, data_buffer.buf, data_buffer.len, self->offset);
 
@@ -257,19 +262,22 @@ PyObject* pysqlite_blob_seek(pysqlite_Blob *self, PyObject *args)
             offset = self->length + offset;
             break;
         default:
-            return PyErr_Format(PyExc_ValueError,
+            PyErr_SetString(PyExc_ValueError,
                                 "from_what should be 0, 1 or 2");
+            return NULL;
     }
 
     if (offset < 0 || offset > self->length) {
-        return PyErr_Format(PyExc_ValueError, "offset out of blob range");
+        PyErr_SetString(PyExc_ValueError, "offset out of blob range");
+        return NULL;
     }
 
     self->offset = offset;
     Py_RETURN_NONE;
 
 overflow:
-    return PyErr_Format(PyExc_OverflowError, "seek offset result in overflow");
+    PyErr_SetString(PyExc_OverflowError, "seek offset result in overflow");
+    return NULL;
 }
 
 
@@ -332,7 +340,7 @@ static int pysqlite_blob_contains(pysqlite_Blob *self, PyObject *args)
 {
     if (pysqlite_check_blob(self)) {
         PyErr_SetString(PyExc_SystemError,
-                        "Blob don't support cotains operation");
+                        "Blob don't support contains operation");
     }
     return -1;
 }
@@ -407,11 +415,11 @@ static PyObject * pysqlite_blob_subscript(pysqlite_Blob *self, PyObject *item)
             return NULL;
         }
 
-        if (slicelen <= 0)
+        if (slicelen <= 0) {
             return PyBytes_FromStringAndSize("", 0);
-        else if (step == 1)
+        } else if (step == 1) {
             return inner_read(self, slicelen, start);
-        else {
+        } else {
             char *result_buf = (char *)PyMem_Malloc(slicelen);
             char *data_buff = NULL;
             Py_ssize_t cur, i;
@@ -586,7 +594,7 @@ static int pysqlite_blob_ass_subscript(pysqlite_Blob *self, PyObject *item, PyOb
     }
     else {
         PyErr_SetString(PyExc_TypeError,
-                        "mmap indices must be integer");
+                        "Blob indices must be integer");
         return -1;
     }
 }
diff --git a/src/cache.c b/src/cache.c
index 89ee894..1a8a873 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -112,9 +112,8 @@ void pysqlite_cache_dealloc(pysqlite_Cache* self)
     Py_TYPE(self)->tp_free((PyObject*)self);
 }
 
-PyObject* pysqlite_cache_get(pysqlite_Cache* self, PyObject* args)
+PyObject* pysqlite_cache_get(pysqlite_Cache* self, PyObject* key)
 {
-    PyObject* key = args;
     pysqlite_Node* node;
     pysqlite_Node* ptr;
     PyObject* data;
@@ -184,6 +183,9 @@ PyObject* pysqlite_cache_get(pysqlite_Cache* self, PyObject* args)
             }
         }
 
+        /* We cannot replace this by PyObject_CallOneArg() since
+         * PyObject_CallFunction() has a special case when using a
+         * single tuple as argument. */
         data = PyObject_CallFunction(self->factory, "O", key);
 
         if (!data) {
diff --git a/src/connection.c b/src/connection.c
index e2a0d34..77e7482 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -31,8 +31,6 @@
 #include "prepare_protocol.h"
 #include "util.h"
 
-#include "pythread.h"
-
 #define ACTION_FINALIZE 1
 #define ACTION_RESET 2
 
@@ -1833,7 +1831,7 @@ pysqlite_connection_create_collation(pysqlite_Connection* self, PyObject* args)
     const char *uppercase_name_str;
     int rc;
     unsigned int kind;
-    void *data;
+    const void *data;
 
     if (!pysqlite_check_thread(self) || !pysqlite_check_connection(self)) {
         goto finally;
diff --git a/test/dbapi.py b/test/dbapi.py
index 00702d6..68fe46d 100644
--- a/test/dbapi.py
+++ b/test/dbapi.py
@@ -593,7 +593,7 @@ class BlobTests(unittest.TestCase):
         self.assertEqual(self.blob.tell(), 50)
 
     def CheckBlobWriteMoreThenBlobSize(self):
-        with self.assertRaises(sqlite.OperationalError):
+        with self.assertRaises(ValueError):
             self.blob.write(b"a" * 1000)
 
     def CheckBlobReadAfterRowChange(self):