diff --git a/app/models/concerns/geojson_format_validator.rb b/app/models/concerns/geojson_format_validator.rb
index 42950c1e2..2182aa3b3 100644
--- a/app/models/concerns/geojson_format_validator.rb
+++ b/app/models/concerns/geojson_format_validator.rb
@@ -115,8 +115,13 @@ class GeojsonFormatValidator < ActiveModel::EachValidator
     end
 
     def valid_polygon_coordinates?(polygon_coordinates)
-      polygon_coordinates.all? do |ring_coordinates|
-        valid_coordinates_array?(ring_coordinates)
-      end
+      polygon_coordinates.is_a?(Array) &&
+        polygon_coordinates.all? { |ring_coordinates| valid_ring_coordinates?(ring_coordinates) }
+    end
+
+    def valid_ring_coordinates?(ring_coordinates)
+      valid_coordinates_array?(ring_coordinates) &&
+        ring_coordinates.size >= 4 &&
+        ring_coordinates.first == ring_coordinates.last
     end
 end
diff --git a/spec/factories/administration.rb b/spec/factories/administration.rb
index b02cfcb20..21d1e9b60 100644
--- a/spec/factories/administration.rb
+++ b/spec/factories/administration.rb
@@ -25,7 +25,7 @@ FactoryBot.define do
             "type": "Feature",
             "geometry": {
               "type": "Polygon",
-              "coordinates": [[[0.117, 51.513], [0.118, 51.512], [0.119, 51.514]]]
+              "coordinates": [[[0.117, 51.513], [0.118, 51.512], [0.119, 51.514], [0.117, 51.513]]]
             }
           }
         JSON
diff --git a/spec/models/geojson_format_validator_spec.rb b/spec/models/geojson_format_validator_spec.rb
index c4b4780f9..a0a5f4eef 100644
--- a/spec/models/geojson_format_validator_spec.rb
+++ b/spec/models/geojson_format_validator_spec.rb
@@ -217,6 +217,221 @@ describe GeojsonFormatValidator do
     end
   end
 
+  context "Polygon geometry" do
+    it "is not valid with a ring having less than four elements" do
+      record.geojson = <<~JSON
+        {
+          "type": "Polygon",
+          "coordinates": [[
+            [1.23, 4.56],
+            [7.89, 10.11],
+            [1.23, 4.56]
+          ]]
+        }
+      JSON
+
+      expect(record).not_to be_valid
+    end
+
+    it "is not valid with a ring which with different starting and end points" do
+      record.geojson = <<~JSON
+        {
+          "type": "Polygon",
+          "coordinates": [[
+            [1.23, 4.56],
+            [7.89, 10.11],
+            [12.13, 14.15],
+            [16.17, 18.19]
+          ]]
+        }
+      JSON
+
+      expect(record).not_to be_valid
+    end
+
+    it "is valid with one valid ring" do
+      record.geojson = <<~JSON
+        {
+          "type": "Polygon",
+          "coordinates": [[
+            [1.23, 4.56],
+            [7.89, 10.11],
+            [12.13, 14.15],
+            [1.23, 4.56]
+          ]]
+        }
+      JSON
+
+      expect(record).to be_valid
+    end
+
+    it "is valid with multiple valid rings" do
+      record.geojson = <<~JSON
+        {
+          "type": "Polygon",
+          "coordinates": [
+            [
+              [100.0, 0.0],
+              [101.0, 0.0],
+              [101.0, 1.0],
+              [100.0, 1.0],
+              [100.0, 0.0]
+            ],
+            [
+              [100.8, 0.8],
+              [100.8, 0.2],
+              [100.2, 0.2],
+              [100.2, 0.8],
+              [100.8, 0.8]
+            ]
+          ]
+        }
+      JSON
+
+      expect(record).to be_valid
+    end
+
+    it "is not valid with multiple rings if some rings are invalid" do
+      record.geojson = <<~JSON
+        {
+          "type": "Polygon",
+          "coordinates": [
+            [
+              [100.0, 0.0],
+              [101.0, 0.0],
+              [101.0, 1.0],
+              [100.0, 1.0],
+              [100.0, 0.0]
+            ],
+            [
+              [100.8, 0.8],
+              [100.8, 0.2],
+              [100.2, 0.2]
+            ]
+          ]
+        }
+      JSON
+
+      expect(record).not_to be_valid
+    end
+  end
+
+  context "MultiPolygon geometry" do
+    it "is not valid with a one-dimensional array of coordinates" do
+      record.geojson = '{ "type": "MultiPolygon", "coordinates": [1.23, 4.56] }'
+
+      expect(record).not_to be_valid
+    end
+
+    it "is not valid with a two-dimensional array of coordinates" do
+      record.geojson = '{ "type": "MultiPolygon", "coordinates": [[1.23, 4.56], [7.89, 4.56]] }'
+
+      expect(record).not_to be_valid
+    end
+
+    it "is not valid with a three-dimensional polygon coordinates array" do
+      record.geojson = <<~JSON
+        {
+          "type": "MultiPolygon",
+          "coordinates": [[
+            [1.23, 4.56],
+            [7.89, 10.11],
+            [12.13, 14.15],
+            [1.23, 4.56]
+          ]]
+        }
+      JSON
+
+      expect(record).not_to be_valid
+    end
+
+    it "is valid with a valid polygon" do
+      record.geojson = <<~JSON
+        {
+          "type": "MultiPolygon",
+          "coordinates": [[[
+            [1.23, 4.56],
+            [7.89, 10.11],
+            [12.13, 14.15],
+            [1.23, 4.56]
+          ]]]
+        }
+      JSON
+
+      expect(record).to be_valid
+    end
+
+    it "is valid with multiple valid polygons" do
+      record.geojson = <<~JSON
+        {
+          "type": "MultiPolygon",
+          "coordinates": [
+            [
+              [
+                [1.23, 4.56],
+                [7.89, 10.11],
+                [12.13, 14.15],
+                [1.23, 4.56]
+              ]
+            ],
+            [
+              [
+                [100.0, 0.0],
+                [101.0, 0.0],
+                [101.0, 1.0],
+                [100.0, 1.0],
+                [100.0, 0.0]
+              ],
+              [
+                [100.8, 0.8],
+                [100.8, 0.2],
+                [100.2, 0.2],
+                [100.2, 0.8],
+                [100.8, 0.8]
+              ]
+            ]
+          ]
+        }
+      JSON
+
+      expect(record).to be_valid
+    end
+
+    it "is not valid with multiple polygons if some polygons are invalid" do
+      record.geojson = <<~JSON
+        {
+          "type": "MultiPolygon",
+          "coordinates": [
+            [
+              [
+                [1.23, 4.56],
+                [7.89, 10.11],
+                [12.13, 14.15],
+                [1.23, 4.56]
+              ]
+            ],
+            [
+              [
+                [100.0, 0.0],
+                [101.0, 0.0],
+                [101.0, 1.0],
+                [100.0, 1.0],
+                [100.0, 0.0]
+              ],
+              [
+                [100.8, 0.8],
+                [100.8, 0.2],
+                [100.2, 0.2]
+              ]
+            ]
+          ]
+        }
+      JSON
+
+      expect(record).not_to be_valid
+    end
+  end
+
   context "GeometryCollection" do
     it "is not valid if it doesn't contain geometries" do
       record.geojson = '{ "type": "GeometryCollection" }'
diff --git a/spec/system/admin/geozones_spec.rb b/spec/system/admin/geozones_spec.rb
index 37b448d2a..27b9f48f0 100644
--- a/spec/system/admin/geozones_spec.rb
+++ b/spec/system/admin/geozones_spec.rb
@@ -115,7 +115,7 @@ describe "Admin geozones", :admin do
         "type": "Feature",
         "geometry": {
           "type": "Polygon",
-          "coordinates": [[[-0.1, 51.5], [-0.2, 51.4], [-0.3, 51.6]]]
+          "coordinates": [[[-0.1, 51.5], [-0.2, 51.4], [-0.3, 51.6], [-0.1, 51.5]]]
         }
       }
     JSON
@@ -158,7 +158,7 @@ describe "Admin geozones", :admin do
         "type": "Feature",
         "geometry": {
           "type": "Polygon",
-          "coordinates": [[[-0.1, 51.5], [-0.2, 51.4], [-0.3, 51.6]]]
+          "coordinates": [[[-0.1, 51.5], [-0.2, 51.4], [-0.3, 51.6], [-0.1, 51.5]]]
         }
       }
     JSON
diff --git a/spec/system/budgets/investments_spec.rb b/spec/system/budgets/investments_spec.rb
index 45930fe45..87a9ed0b1 100644
--- a/spec/system/budgets/investments_spec.rb
+++ b/spec/system/budgets/investments_spec.rb
@@ -1661,7 +1661,7 @@ describe "Budget Investments" do
           "type": "Feature",
           "geometry": {
             "type": "Polygon",
-            "coordinates": [[[-0.1, 51.5], [-0.2, 51.4], [-0.3, 51.6]]]
+            "coordinates": [[[-0.1, 51.5], [-0.2, 51.4], [-0.3, 51.6], [-0.1, 51.5]]]
           }
         }
       JSON
@@ -1671,7 +1671,7 @@ describe "Budget Investments" do
           "type": "Feature",
           "geometry": {
             "type": "Polygon",
-            "coordinates": [[[-0.1, 51.5], [-0.2, 51.5], [-0.2, 51.6], [-0.1, 51.6]]]
+            "coordinates": [[[-0.1, 51.5], [-0.2, 51.5], [-0.2, 51.6], [-0.1, 51.6], [-0.1, 51.5]]]
           }
         }
       JSON