diff --git a/src/connection.c b/src/connection.c
index 0ba66b2..376502e 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -1376,7 +1376,7 @@ PyObject* pysqlite_connection_call(pysqlite_Connection* self, PyObject* args, Py
     if (!_PyArg_NoKeywords(MODULE_NAME ".Connection", kwargs))
         return NULL;
 
-    if (!PyArg_ParseTuple(args, "O", &sql))
+    if (!PyArg_ParseTuple(args, "U", &sql))
         return NULL;
 
     _pysqlite_drop_unused_statement_references(self);
diff --git a/src/cursor.c b/src/cursor.c
index 2bc1931..69f8a60 100644
--- a/src/cursor.c
+++ b/src/cursor.c
@@ -384,12 +384,7 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* args)
 
     if (multiple) {
         /* executemany() */
-        if (!PyArg_ParseTuple(args, "OO", &operation, &second_argument)) {
-            goto error;
-        }
-
-        if (!PyUnicode_Check(operation)) {
-            PyErr_SetString(PyExc_ValueError, "operation parameter must be str");
+        if (!PyArg_ParseTuple(args, "UO", &operation, &second_argument)) {
             goto error;
         }
 
@@ -406,12 +401,7 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* args)
         }
     } else {
         /* execute() */
-        if (!PyArg_ParseTuple(args, "O|O", &operation, &second_argument)) {
-            goto error;
-        }
-
-        if (!PyUnicode_Check(operation)) {
-            PyErr_SetString(PyExc_ValueError, "operation parameter must be str");
+        if (!PyArg_ParseTuple(args, "U|O", &operation, &second_argument)) {
             goto error;
         }
 
diff --git a/src/statement.c b/src/statement.c
index 7f58b9a..fb1b8bd 100644
--- a/src/statement.c
+++ b/src/statement.c
@@ -59,6 +59,8 @@ int pysqlite_statement_create(pysqlite_Statement* self, pysqlite_Connection* con
     self->st = NULL;
     self->in_use = 0;
 
+    assert(PyUnicode_Check(sql));
+
     sql_cstr = PyUnicode_AsUTF8AndSize(sql, &sql_cstr_len);
     if (sql_cstr == NULL) {
         rc = PYSQLITE_SQL_WRONG_TYPE;
diff --git a/test/dbapi.py b/test/dbapi.py
index bdfd496..6249828 100644
--- a/test/dbapi.py
+++ b/test/dbapi.py
@@ -232,7 +232,7 @@ class CursorTests(unittest.TestCase):
             """)
 
     def CheckExecuteWrongSqlArg(self):
-        with self.assertRaises(ValueError):
+        with self.assertRaises(TypeError):
             self.cu.execute(42)
 
     def CheckExecuteArgInt(self):
@@ -379,7 +379,7 @@ class CursorTests(unittest.TestCase):
         self.cu.executemany("insert into test(income) values (?)", mygen())
 
     def CheckExecuteManyWrongSqlArg(self):
-        with self.assertRaises(ValueError):
+        with self.assertRaises(TypeError):
             self.cu.executemany(42, [(3,)])
 
     def CheckExecuteManySelect(self):
diff --git a/test/regression.py b/test/regression.py
index d676953..d8aebcc 100644
--- a/test/regression.py
+++ b/test/regression.py
@@ -262,7 +262,7 @@ class RegressionTests(unittest.TestCase):
         Call a connection with a non-string SQL request: check error handling
         of the statement constructor.
         """
-        self.assertRaises(sqlite.Warning, self.con, 1)
+        self.assertRaises(TypeError, self.con, 1)
 
     def CheckCollation(self):
         def collation_cb(a, b):