diff --git a/django/contrib/gis/forms/widgets.py b/django/contrib/gis/forms/widgets.py
index aba16f874a..53853b84f3 100644
--- a/django/contrib/gis/forms/widgets.py
+++ b/django/contrib/gis/forms/widgets.py
@@ -35,7 +35,7 @@ class BaseGeometryWidget(Widget):
 
     def deserialize(self, value):
         try:
-            return GEOSGeometry(value, self.map_srid)
+            return GEOSGeometry(value)
         except (GEOSException, ValueError) as err:
             logger.error("Error creating geometry from value '%s' (%s)", value, err)
         return None
@@ -48,7 +48,7 @@ class BaseGeometryWidget(Widget):
 
         if value:
             # Check that srid of value and map match
-            if value.srid != self.map_srid:
+            if value.srid and value.srid != self.map_srid:
                 try:
                     ogr = value.ogr
                     ogr.transform(self.map_srid)
diff --git a/django/contrib/gis/geos/geometry.py b/django/contrib/gis/geos/geometry.py
index 55cc2614ad..8e0719f4fa 100644
--- a/django/contrib/gis/geos/geometry.py
+++ b/django/contrib/gis/geos/geometry.py
@@ -46,6 +46,7 @@ class GEOSGeometry(GEOSBase, ListMixin):
         The `srid` keyword is used to specify the Source Reference Identifier
         (SRID) number for this Geometry.  If not set, the SRID will be None.
         """
+        input_srid = None
         if isinstance(geo_input, bytes):
             geo_input = force_text(geo_input)
         if isinstance(geo_input, str):
@@ -53,7 +54,7 @@ class GEOSGeometry(GEOSBase, ListMixin):
             if wkt_m:
                 # Handling WKT input.
                 if wkt_m.group('srid'):
-                    srid = int(wkt_m.group('srid'))
+                    input_srid = int(wkt_m.group('srid'))
                 g = wkt_r().read(force_bytes(wkt_m.group('wkt')))
             elif hex_regex.match(geo_input):
                 # Handling HEXEWKB input.
@@ -75,14 +76,17 @@ class GEOSGeometry(GEOSBase, ListMixin):
             # Invalid geometry type.
             raise TypeError('Improper geometry input type: %s' % type(geo_input))
 
-        if g:
-            # Setting the pointer object with a valid pointer.
-            self.ptr = g
-        else:
+        if not g:
             raise GEOSException('Could not initialize GEOS Geometry with given input.')
 
+        input_srid = input_srid or capi.geos_get_srid(g) or None
+        if input_srid and srid and input_srid != srid:
+            raise ValueError('Input geometry already has SRID: %d.' % input_srid)
+
+        # Setting the pointer object with a valid pointer.
+        self.ptr = g
         # Post-initialization setup.
-        self._post_init(srid)
+        self._post_init(input_srid or srid)
 
     def _post_init(self, srid):
         "Perform post-initialization setup."
diff --git a/docs/ref/contrib/gis/geos.txt b/docs/ref/contrib/gis/geos.txt
index 68c4a2ac30..0c8139d218 100644
--- a/docs/ref/contrib/gis/geos.txt
+++ b/docs/ref/contrib/gis/geos.txt
@@ -194,6 +194,27 @@ This is the base class for all GEOS geometry objects.  It initializes on the
 given ``geo_input`` argument, and then assumes the proper geometry subclass
 (e.g., ``GEOSGeometry('POINT(1 1)')`` will create a :class:`Point` object).
 
+The ``srid`` parameter, if given, is set as the SRID of the created geometry if
+``geo_input`` doesn't have an SRID. If different SRIDs are provided through the
+``geo_input`` and ``srid`` parameters, ``ValueError`` is raised::
+
+    >>> from django.contrib.gis.geos import GEOSGeometry
+    >>> GEOSGeometry('POINT EMPTY', srid=4326).ewkt
+    'SRID=4326;POINT EMPTY'
+    >>> GEOSGeometry('SRID=4326;POINT EMPTY', srid=4326).ewkt
+    'SRID=4326;POINT EMPTY'
+    >>> GEOSGeometry('SRID=1;POINT EMPTY', srid=4326)
+    Traceback (most recent call last):
+    ...
+    ValueError: Input geometry already has SRID: 1.
+
+.. versionchanged:: 2.0
+
+    In older versions, the ``srid`` parameter is handled differently for WKT
+    and WKB input. For WKT, ``srid`` is used only if the input geometry doesn't
+    have an SRID. For WKB, ``srid`` (if given) replaces the SRID of the input
+    geometry.
+
 The following input formats, along with their corresponding Python types,
 are accepted:
 
diff --git a/tests/gis_tests/geos_tests/test_geos.py b/tests/gis_tests/geos_tests/test_geos.py
index 53e42e4b2f..72d035cc22 100644
--- a/tests/gis_tests/geos_tests/test_geos.py
+++ b/tests/gis_tests/geos_tests/test_geos.py
@@ -708,6 +708,14 @@ class GEOSTest(SimpleTestCase, TestDataMixin):
         pnt_wo_srid = Point(1, 1)
         pnt_wo_srid.srid = pnt_wo_srid.srid
 
+        # Input geometries that have an SRID.
+        self.assertEqual(GEOSGeometry(pnt.ewkt, srid=pnt.srid).srid, pnt.srid)
+        self.assertEqual(GEOSGeometry(pnt.ewkb, srid=pnt.srid).srid, pnt.srid)
+        with self.assertRaisesMessage(ValueError, 'Input geometry already has SRID: %d.' % pnt.srid):
+            GEOSGeometry(pnt.ewkt, srid=1)
+        with self.assertRaisesMessage(ValueError, 'Input geometry already has SRID: %d.' % pnt.srid):
+            GEOSGeometry(pnt.ewkb, srid=1)
+
     @skipUnless(HAS_GDAL, "GDAL is required.")
     def test_custom_srid(self):
         """Test with a null srid and a srid unknown to GDAL."""