diff --git a/ChangeLog b/ChangeLog
index fbf7cc83..bb7014df 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2008-01-22  James Henstridge  <james@jamesh.id.au>
+
+	* psycopg/*.[ch]: add const qualifier to various string arguments
+	to functions (typecast functions and conn_switch_isolation_level).
+
 2008-01-21  James Henstridge  <james@jamesh.id.au>
 
 	* setup.cfg (define): remove PSYCOPG_DISPLAY_SIZE from default
diff --git a/psycopg/connection.h b/psycopg/connection.h
index e4ef2f11..18674643 100644
--- a/psycopg/connection.h
+++ b/psycopg/connection.h
@@ -83,7 +83,7 @@ HIDDEN void conn_close(connectionObject *self);
 HIDDEN int  conn_commit(connectionObject *self);
 HIDDEN int  conn_rollback(connectionObject *self);
 HIDDEN int  conn_switch_isolation_level(connectionObject *self, int level);
-HIDDEN int  conn_set_client_encoding(connectionObject *self, char *enc);
+HIDDEN int  conn_set_client_encoding(connectionObject *self, const char *enc);
 
 /* exception-raising macros */
 #define EXC_IF_CONN_CLOSED(self) if ((self)->closed > 0) { \
diff --git a/psycopg/connection_int.c b/psycopg/connection_int.c
index bf72df3e..2cc7818e 100644
--- a/psycopg/connection_int.c
+++ b/psycopg/connection_int.c
@@ -296,7 +296,7 @@ conn_switch_isolation_level(connectionObject *self, int level)
 /* conn_set_client_encoding - switch client encoding on connection */
 
 int
-conn_set_client_encoding(connectionObject *self, char *enc)
+conn_set_client_encoding(connectionObject *self, const char *enc)
 {
     PGresult *pgres = NULL;
     char *error = NULL;
diff --git a/psycopg/typecast.c b/psycopg/typecast.c
index 8d6df5bf..75ab293a 100644
--- a/psycopg/typecast.c
+++ b/psycopg/typecast.c
@@ -32,15 +32,15 @@
 
 /* usefull function used by some typecasters */
 
-static char *
-skip_until_space(char *s)
+static const char *
+skip_until_space(const char *s)
 {
     while (*s && *s != ' ') s++;
     return s;
 }
 
-static char *
-skip_until_space2(char *s, Py_ssize_t *len)
+static const char *
+skip_until_space2(const char *s, Py_ssize_t *len)
 {
     while (*len > 0 && *s && *s != ' ') {
         s++; (*len)--;
@@ -49,7 +49,7 @@ skip_until_space2(char *s, Py_ssize_t *len)
 }
 
 static int
-typecast_parse_date(char* s, char** t, Py_ssize_t* len,
+typecast_parse_date(const char* s, const char** t, Py_ssize_t* len,
                      int* year, int* month, int* day)
 {
     int acc = -1, cz = 0;
@@ -92,7 +92,7 @@ typecast_parse_date(char* s, char** t, Py_ssize_t* len,
 }
 
 static int
-typecast_parse_time(char* s, char** t, Py_ssize_t* len,
+typecast_parse_time(const char* s, const char** t, Py_ssize_t* len,
                      int* hh, int* mm, int* ss, int* us, int* tz)
 {
     int acc = -1, cz = 0;
@@ -556,7 +556,7 @@ typecast_from_c(typecastObject_initlist *type, PyObject *dict)
 }
 
 PyObject *
-typecast_cast(PyObject *obj, char *str, Py_ssize_t len, PyObject *curs)
+typecast_cast(PyObject *obj, const char *str, Py_ssize_t len, PyObject *curs)
 {
     PyObject *old, *res = NULL;
     typecastObject *self = (typecastObject *)obj;
diff --git a/psycopg/typecast.h b/psycopg/typecast.h
index c64bc309..17e5486f 100644
--- a/psycopg/typecast.h
+++ b/psycopg/typecast.h
@@ -32,7 +32,8 @@ extern "C" {
 #endif
 
 /* type of type-casting functions (both C and Python) */
-typedef PyObject *(*typecast_function)(char *, Py_ssize_t len, PyObject *);
+typedef PyObject *(*typecast_function)(const char *str, Py_ssize_t len,
+                                       PyObject *cursor);
 
 /** typecast type **/
 
@@ -83,6 +84,6 @@ HIDDEN PyObject *typecast_from_python(
 
 /* the function used to dispatch typecasting calls */
 HIDDEN PyObject *typecast_cast(
-    PyObject *self, char *str, Py_ssize_t len, PyObject *curs);
+    PyObject *self, const char *str, Py_ssize_t len, PyObject *curs);
 
 #endif /* !defined(PSYCOPG_TYPECAST_H) */
diff --git a/psycopg/typecast_array.c b/psycopg/typecast_array.c
index 4a792266..b05c6345 100644
--- a/psycopg/typecast_array.c
+++ b/psycopg/typecast_array.c
@@ -24,7 +24,7 @@
 /** typecast_array_cleanup - remove the horrible [...]= stuff **/
 
 static int
-typecast_array_cleanup(char **str, Py_ssize_t *len)
+typecast_array_cleanup(const char **str, Py_ssize_t *len)
 {
     Py_ssize_t i, depth = 1;
 
@@ -53,7 +53,7 @@ typecast_array_cleanup(char **str, Py_ssize_t *len)
 #define ASCAN_QUOTED 4
 
 static int
-typecast_array_tokenize(char *str, Py_ssize_t strlength,
+typecast_array_tokenize(const char *str, Py_ssize_t strlength,
                         Py_ssize_t *pos, char** token,
                         Py_ssize_t *length, int *quotes)
 {
@@ -148,7 +148,7 @@ typecast_array_tokenize(char *str, Py_ssize_t strlength,
         *length = (Py_ssize_t) (buffer - *token);
     }
     else {
-        *token = &str[*pos];
+        *token = (char *)&str[*pos];
         *length = l;
     }
 
@@ -161,7 +161,7 @@ typecast_array_tokenize(char *str, Py_ssize_t strlength,
 }
 
 static int
-typecast_array_scan(char *str, Py_ssize_t strlength,
+typecast_array_scan(const char *str, Py_ssize_t strlength,
                     PyObject *curs, PyObject *base, PyObject *array)
 {
     int state, quotes = 0;
@@ -235,7 +235,7 @@ typecast_array_scan(char *str, Py_ssize_t strlength,
     have to be taken on the single items **/
 
 static PyObject *
-typecast_GENERIC_ARRAY_cast(char *str, Py_ssize_t len, PyObject *curs)
+typecast_GENERIC_ARRAY_cast(const char *str, Py_ssize_t len, PyObject *curs)
 {
     PyObject *obj = NULL;
     PyObject *base = ((typecastObject*)((cursorObject*)curs)->caster)->bcast;
diff --git a/psycopg/typecast_basic.c b/psycopg/typecast_basic.c
index eeb96be9..c4f3cf62 100644
--- a/psycopg/typecast_basic.c
+++ b/psycopg/typecast_basic.c
@@ -22,7 +22,7 @@
 /** INTEGER - cast normal integers (4 bytes) to python int **/
 
 static PyObject *
-typecast_INTEGER_cast(char *s, Py_ssize_t len, PyObject *curs)
+typecast_INTEGER_cast(const char *s, Py_ssize_t len, PyObject *curs)
 {
     char buffer[12];
 
@@ -31,13 +31,13 @@ typecast_INTEGER_cast(char *s, Py_ssize_t len, PyObject *curs)
         strncpy(buffer, s, (size_t) len); buffer[len] = '\0';
         s = buffer;
     }
-    return PyInt_FromString(s, NULL, 0);
+    return PyInt_FromString((char *)s, NULL, 0);
 }
 
 /** LONGINTEGER - cast long integers (8 bytes) to python long **/
 
 static PyObject *
-typecast_LONGINTEGER_cast(char *s, Py_ssize_t len, PyObject *curs)
+typecast_LONGINTEGER_cast(const char *s, Py_ssize_t len, PyObject *curs)
 {
     char buffer[24];
 
@@ -46,13 +46,13 @@ typecast_LONGINTEGER_cast(char *s, Py_ssize_t len, PyObject *curs)
         strncpy(buffer, s, (size_t) len); buffer[len] = '\0';
         s = buffer;
     }
-    return PyLong_FromString(s, NULL, 0);
+    return PyLong_FromString((char *)s, NULL, 0);
 }
 
 /** FLOAT - cast floating point numbers to python float **/
 
 static PyObject *
-typecast_FLOAT_cast(char *s, Py_ssize_t len, PyObject *curs)
+typecast_FLOAT_cast(const char *s, Py_ssize_t len, PyObject *curs)
 {
     PyObject *str = NULL, *flo = NULL;
     char *pend;
@@ -67,7 +67,7 @@ typecast_FLOAT_cast(char *s, Py_ssize_t len, PyObject *curs)
 /** STRING - cast strings of any type to python string **/
 
 static PyObject *
-typecast_STRING_cast(char *s, Py_ssize_t len, PyObject *curs)
+typecast_STRING_cast(const char *s, Py_ssize_t len, PyObject *curs)
 {
     if (s == NULL) {Py_INCREF(Py_None); return Py_None;}
     return PyString_FromStringAndSize(s, len);
@@ -76,7 +76,7 @@ typecast_STRING_cast(char *s, Py_ssize_t len, PyObject *curs)
 /** UNICODE - cast strings of any type to a python unicode object **/
 
 static PyObject *
-typecast_UNICODE_cast(char *s, Py_ssize_t len, PyObject *curs)
+typecast_UNICODE_cast(const char *s, Py_ssize_t len, PyObject *curs)
 {
     PyObject *enc;
 
@@ -98,7 +98,7 @@ typecast_UNICODE_cast(char *s, Py_ssize_t len, PyObject *curs)
 /** BOOLEAN - cast boolean value into right python object **/
 
 static PyObject *
-typecast_BOOLEAN_cast(char *s, Py_ssize_t len, PyObject *curs)
+typecast_BOOLEAN_cast(const char *s, Py_ssize_t len, PyObject *curs)
 {
     PyObject *res;
 
@@ -117,7 +117,7 @@ typecast_BOOLEAN_cast(char *s, Py_ssize_t len, PyObject *curs)
 
 #ifdef HAVE_DECIMAL
 static PyObject *
-typecast_DECIMAL_cast(char *s, Py_ssize_t len, PyObject *curs)
+typecast_DECIMAL_cast(const char *s, Py_ssize_t len, PyObject *curs)
 {
     PyObject *res = NULL;
     PyObject *decimalType;
diff --git a/psycopg/typecast_binary.c b/psycopg/typecast_binary.c
index 52674dda..47fff1ee 100644
--- a/psycopg/typecast_binary.c
+++ b/psycopg/typecast_binary.c
@@ -156,7 +156,7 @@ typecast_BINARY_cast_unescape(unsigned char *str, size_t *to_length)
 #endif
 
 static PyObject *
-typecast_BINARY_cast(char *s, Py_ssize_t l, PyObject *curs)
+typecast_BINARY_cast(const char *s, Py_ssize_t l, PyObject *curs)
 {
     chunkObject *chunk = NULL;
     PyObject *res = NULL;
diff --git a/psycopg/typecast_datetime.c b/psycopg/typecast_datetime.c
index f8b4f1fb..6748c6a6 100644
--- a/psycopg/typecast_datetime.c
+++ b/psycopg/typecast_datetime.c
@@ -34,7 +34,7 @@ extern PyObject *pyDeltaTypeP;
 /** DATE - cast a date into a date python object **/
 
 static PyObject *
-typecast_PYDATE_cast(char *str, Py_ssize_t len, PyObject *curs)
+typecast_PYDATE_cast(const char *str, Py_ssize_t len, PyObject *curs)
 {
     PyObject* obj = NULL;
     int n, y=0, m=0, d=0;
@@ -70,12 +70,12 @@ typecast_PYDATE_cast(char *str, Py_ssize_t len, PyObject *curs)
 /** DATETIME - cast a timestamp into a datetime python object **/
 
 static PyObject *
-typecast_PYDATETIME_cast(char *str, Py_ssize_t len, PyObject *curs)
+typecast_PYDATETIME_cast(const char *str, Py_ssize_t len, PyObject *curs)
 {
     PyObject* obj = NULL;
     int n, y=0, m=0, d=0;
     int hh=0, mm=0, ss=0, us=0, tz=0;
-    char *tp = NULL;
+    const char *tp = NULL;
 
     if (str == NULL) {Py_INCREF(Py_None); return Py_None;}
 
@@ -144,7 +144,7 @@ typecast_PYDATETIME_cast(char *str, Py_ssize_t len, PyObject *curs)
 /** TIME - parse time into a time object **/
 
 static PyObject *
-typecast_PYTIME_cast(char *str, Py_ssize_t len, PyObject *curs)
+typecast_PYTIME_cast(const char *str, Py_ssize_t len, PyObject *curs)
 {
     PyObject* obj = NULL;
     int n, hh=0, mm=0, ss=0, us=0, tz=0;
@@ -172,7 +172,7 @@ typecast_PYTIME_cast(char *str, Py_ssize_t len, PyObject *curs)
 /** INTERVAL - parse an interval into a timedelta object **/
 
 static PyObject *
-typecast_PYINTERVAL_cast(char *str, Py_ssize_t len, PyObject *curs)
+typecast_PYINTERVAL_cast(const char *str, Py_ssize_t len, PyObject *curs)
 {
     long years = 0, months = 0, days = 0;
     double hours = 0.0, minutes = 0.0, seconds = 0.0, hundredths = 0.0;
diff --git a/psycopg/typecast_mxdatetime.c b/psycopg/typecast_mxdatetime.c
index 85809da4..bdd2955b 100644
--- a/psycopg/typecast_mxdatetime.c
+++ b/psycopg/typecast_mxdatetime.c
@@ -28,11 +28,11 @@ extern mxDateTimeModule_APIObject *mxDateTimeP;
 /** DATE - cast a date into mx.DateTime python object **/
 
 static PyObject *
-typecast_MXDATE_cast(char *str, Py_ssize_t len, PyObject *curs)
+typecast_MXDATE_cast(const char *str, Py_ssize_t len, PyObject *curs)
 {
     int n, y=0, m=0, d=0;
     int hh=0, mm=0, ss=0, us=0, tz=0;
-    char *tp = NULL;
+    const char *tp = NULL;
 
     if (str == NULL) {Py_INCREF(Py_None); return Py_None;}
 
@@ -76,7 +76,7 @@ typecast_MXDATE_cast(char *str, Py_ssize_t len, PyObject *curs)
 /** TIME - parse time into an mx.DateTime object **/
 
 static PyObject *
-typecast_MXTIME_cast(char *str, Py_ssize_t len, PyObject *curs)
+typecast_MXTIME_cast(const char *str, Py_ssize_t len, PyObject *curs)
 {
     int n, hh=0, mm=0, ss=0, us=0, tz=0;
 
@@ -103,7 +103,7 @@ typecast_MXTIME_cast(char *str, Py_ssize_t len, PyObject *curs)
 /** INTERVAL - parse an interval into an mx.DateTimeDelta **/
 
 static PyObject *
-typecast_MXINTERVAL_cast(char *str, Py_ssize_t len, PyObject *curs)
+typecast_MXINTERVAL_cast(const char *str, Py_ssize_t len, PyObject *curs)
 {
     long years = 0, months = 0, days = 0, denominator = 1;
     double hours = 0.0, minutes = 0.0, seconds = 0.0, hundredths = 0.0;