diff --git a/psycopg/config.h b/psycopg/config.h
index a2501096..be5e39d3 100644
--- a/psycopg/config.h
+++ b/psycopg/config.h
@@ -66,8 +66,8 @@ static void Dprintf(const char *fmt, ...) {}
 #include <winsock2.h>
 #define pthread_mutex_t HANDLE
 #define pthread_condvar_t HANDLE
-#define pthread_mutex_lock(object) WaitForSingleObject(object, INFINITE)
-#define pthread_mutex_unlock(object) ReleaseMutex(object)
+#define pthread_mutex_lock(object) WaitForSingleObject(*(object), INFINITE)
+#define pthread_mutex_unlock(object) ReleaseMutex(*(object))
 #define pthread_mutex_destroy(ref) (CloseHandle(*(ref)))
 /* convert pthread mutex to native mutex */
 static int pthread_mutex_init(pthread_mutex_t *mutex, void* fake)
diff --git a/psycopg/cursor_type.c b/psycopg/cursor_type.c
index bcbae3fc..0da50cf5 100644
--- a/psycopg/cursor_type.c
+++ b/psycopg/cursor_type.c
@@ -308,15 +308,18 @@ _psyco_curs_execute(cursorObject *self,
     int res = 0;
     PyObject *fquery, *cvt = NULL;
 
+    Py_BEGIN_ALLOW_THREADS;
     pthread_mutex_lock(&(self->conn->lock));
     if (self->conn->async_cursor != NULL
         && self->conn->async_cursor != (PyObject*)self) {
         pthread_mutex_unlock(&(self->conn->lock));
+        Py_BLOCK_THREADS;
         psyco_set_error(ProgrammingError, (PyObject*)self,
                          "asynchronous query already in execution", NULL, NULL);
         return 0;
     }
     pthread_mutex_unlock(&(self->conn->lock));
+    Py_END_ALLOW_THREADS;
 
     operation = _psyco_curs_validate_sql_basic(self, operation);
 
@@ -641,15 +644,18 @@ _psyco_curs_prefetch(cursorObject *self)
 
     /* check if the fetching cursor is the one that did the asynchronous query
        and raise an exception if not */
+    Py_BEGIN_ALLOW_THREADS;
     pthread_mutex_lock(&(self->conn->lock));
     if (self->conn->async_cursor != NULL
         && self->conn->async_cursor != (PyObject*)self) {
         pthread_mutex_unlock(&(self->conn->lock));
+        Py_BLOCK_THREADS;
         psyco_set_error(ProgrammingError, (PyObject*)self,
                          "asynchronous fetch by wrong cursor", NULL, NULL);
         return -2;
     }
     pthread_mutex_unlock(&(self->conn->lock));
+    Py_END_ALLOW_THREADS;
 
     if (self->pgres == NULL || self->needsfetch) {
         self->needsfetch = 0;
@@ -1382,12 +1388,12 @@ psyco_curs_fileno(cursorObject *self, PyObject *args)
 
     /* note how we call PQflush() to make sure the user will use
        select() in the safe way! */
-    pthread_mutex_lock(&(self->conn->lock));
     Py_BEGIN_ALLOW_THREADS;
+    pthread_mutex_lock(&(self->conn->lock));
     PQflush(self->conn->pgconn);
     socket = (long int)PQsocket(self->conn->pgconn);
-    Py_END_ALLOW_THREADS;
     pthread_mutex_unlock(&(self->conn->lock));
+    Py_END_ALLOW_THREADS;
 
     return PyInt_FromLong(socket);
 }
@@ -1413,10 +1419,12 @@ psyco_curs_isready(cursorObject *self, PyObject *args)
     }
     else {
         IFCLEARPGRES(self->pgres);
+        Py_BEGIN_ALLOW_THREADS;
         pthread_mutex_lock(&(self->conn->lock));
         self->pgres = PQgetResult(self->conn->pgconn);
         self->conn->async_cursor = NULL;
         pthread_mutex_unlock(&(self->conn->lock));
+        Py_END_ALLOW_THREADS;
         self->needsfetch = 1;
         Py_INCREF(Py_True);
         return Py_True;
diff --git a/psycopg/pqpath.c b/psycopg/pqpath.c
index 46fde60b..ae7d65c6 100644
--- a/psycopg/pqpath.c
+++ b/psycopg/pqpath.c
@@ -564,11 +564,12 @@ _pq_fetch_tuples(cursorObject *curs)
         int fsize = PQfsize(curs->pgres, i);
         int fmod =  PQfmod(curs->pgres, i);
 
-        Py_BLOCK_THREADS;
         PyObject *dtitem = PyTuple_New(7);
         PyObject *type = PyInt_FromLong(ftype);
         PyObject *cast = NULL;
 
+        Py_BLOCK_THREADS;
+
         PyTuple_SET_ITEM(curs->description, i, dtitem);
 
         /* fill the right cast function by accessing three different dictionaries:
diff --git a/psycopg/psycopgmodule.c b/psycopg/psycopgmodule.c
index 43b9ea38..2c4be8ce 100644
--- a/psycopg/psycopgmodule.c
+++ b/psycopg/psycopgmodule.c
@@ -593,6 +593,7 @@ psyco_GetDecimalType(void)
     static PyObject *cachedType = NULL;
 
 #ifdef HAVE_DECIMAL
+    PyObject *decimal = PyImport_ImportModule("decimal");
 
     /* Use the cached object if running from the main interpreter. */
     int can_cache = psyco_is_main_interp();
@@ -602,7 +603,6 @@ psyco_GetDecimalType(void)
     }
 
     /* Get a new reference to the Decimal type. */
-    PyObject *decimal = PyImport_ImportModule("decimal");
     if (decimal) {
         decimalType = PyObject_GetAttrString(decimal, "Decimal");
         Py_DECREF(decimal);