diff --git a/NEWS b/NEWS
index ef24fbcc..76333959 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,7 @@ What's new in psycopg 2.8.6
 - Fixed memory leak changing connection encoding to the current one
   (:ticket:`#1101`).
 - Fixed search of mxDateTime headers in virtualenvs (:ticket:`#996`).
+- Added missing values from errorcodes (:ticket:`#1133`).
 - Wheel package compiled against OpenSSL 1.1.1g.
 
 
diff --git a/lib/errorcodes.py b/lib/errorcodes.py
index fc5261ad..38bc7081 100644
--- a/lib/errorcodes.py
+++ b/lib/errorcodes.py
@@ -43,7 +43,8 @@ def lookup(code, _cache={}):
     tmp = {}
     for k, v in globals().items():
         if isinstance(v, str) and len(v) in (2, 5):
-            tmp[v] = k
+            # Strip trailing underscore used to disambiguate duplicate values
+            tmp[v] = k.rstrip("_")
 
     assert tmp
 
@@ -106,7 +107,7 @@ SUCCESSFUL_COMPLETION = '00000'
 # Class 01 - Warning
 WARNING = '01000'
 NULL_VALUE_ELIMINATED_IN_SET_FUNCTION = '01003'
-STRING_DATA_RIGHT_TRUNCATION = '01004'
+STRING_DATA_RIGHT_TRUNCATION_ = '01004'
 PRIVILEGE_NOT_REVOKED = '01006'
 PRIVILEGE_NOT_GRANTED = '01007'
 IMPLICIT_ZERO_BIT_PADDING = '01008'
@@ -164,7 +165,7 @@ DATA_EXCEPTION = '22000'
 STRING_DATA_RIGHT_TRUNCATION = '22001'
 NULL_VALUE_NO_INDICATOR_PARAMETER = '22002'
 NUMERIC_VALUE_OUT_OF_RANGE = '22003'
-NULL_VALUE_NOT_ALLOWED = '22004'
+NULL_VALUE_NOT_ALLOWED_ = '22004'
 ERROR_IN_ASSIGNMENT = '22005'
 INVALID_DATETIME_FORMAT = '22007'
 DATETIME_FIELD_OVERFLOW = '22008'
@@ -273,9 +274,9 @@ INVALID_TRANSACTION_TERMINATION = '2D000'
 
 # Class 2F - SQL Routine Exception
 SQL_ROUTINE_EXCEPTION = '2F000'
-MODIFYING_SQL_DATA_NOT_PERMITTED = '2F002'
-PROHIBITED_SQL_STATEMENT_ATTEMPTED = '2F003'
-READING_SQL_DATA_NOT_PERMITTED = '2F004'
+MODIFYING_SQL_DATA_NOT_PERMITTED_ = '2F002'
+PROHIBITED_SQL_STATEMENT_ATTEMPTED_ = '2F003'
+READING_SQL_DATA_NOT_PERMITTED_ = '2F004'
 FUNCTION_EXECUTED_NO_RETURN_STATEMENT = '2F005'
 
 # Class 34 - Invalid Cursor Name
diff --git a/scripts/make_errorcodes.py b/scripts/make_errorcodes.py
index 26269c7e..118ff2f6 100755
--- a/scripts/make_errorcodes.py
+++ b/scripts/make_errorcodes.py
@@ -36,6 +36,8 @@ def main():
     classes, errors = fetch_errors(
         ['9.1', '9.2', '9.3', '9.4', '9.5', '9.6', '10', '11', '12'])
 
+    disambiguate(errors)
+
     f = open(filename, "w")
     for line in file_start:
         print(line, file=f)
@@ -116,6 +118,18 @@ def fetch_errors(versions):
     return classes, errors
 
 
+def disambiguate(errors):
+    """
+    Change name for exception defined more than once.
+
+    Change the first occurrence, because before introdcing the function
+    they were pretty much lost (see ticket #1133)
+    """
+    # Note: if some code is missing it will be caught downstream
+    for code in "01004 22004 2F002 2F003 2F004".split():
+        errors[code[:2]][code] += "_"
+
+
 def generate_module_data(classes, errors):
     yield ""
     yield "# Error classes"
@@ -124,11 +138,16 @@ def generate_module_data(classes, errors):
             .strip().replace(" ", "_").replace('/', "_").upper()
         yield "CLASS_%s = %r" % (err, clscode)
 
+    seen = set()
+
     for clscode, clslabel in sorted(classes.items()):
         yield ""
         yield "# %s" % clslabel
 
         for errcode, errlabel in sorted(errors[clscode].items()):
+            if errlabel in seen:
+                raise Exception("error label already seen: %s" % errlabel)
+            seen.add(errlabel)
             yield "%s = %r" % (errlabel, errcode)
 
 
diff --git a/tests/test_errcodes.py b/tests/test_errcodes.py
index 3074bae1..3ce3282e 100755
--- a/tests/test_errcodes.py
+++ b/tests/test_errcodes.py
@@ -57,6 +57,14 @@ class ErrocodeTests(ConnectingTestCase):
                         len(errs), MAX_CYCLES,
                         errs[0].__class__.__name__, errs[0]))
 
+    def test_ambiguous_names(self):
+        self.assertEqual(
+            errorcodes.lookup('2F004'), "READING_SQL_DATA_NOT_PERMITTED")
+        self.assertEqual(
+            errorcodes.lookup('38004'), "READING_SQL_DATA_NOT_PERMITTED")
+        self.assertEqual(errorcodes.READING_SQL_DATA_NOT_PERMITTED, '38004')
+        self.assertEqual(errorcodes.READING_SQL_DATA_NOT_PERMITTED_, '2F004')
+
 
 def test_suite():
     return unittest.TestLoader().loadTestsFromName(__name__)