diff --git a/lib/pleroma/upload.ex b/lib/pleroma/upload.ex
index 1d8b073af..b19920dff 100644
--- a/lib/pleroma/upload.ex
+++ b/lib/pleroma/upload.ex
@@ -219,6 +219,7 @@ defp url_from_spec(base_url, {:file, path}) do
       path
       |> URI.encode()
       |> String.replace("?", "%3F")
+      |> String.replace(":", "%3A")
 
     [base_url, "media", path]
     |> Path.join()
diff --git a/test/upload_test.exs b/test/upload_test.exs
index ffef74270..b2d9eca38 100644
--- a/test/upload_test.exs
+++ b/test/upload_test.exs
@@ -153,19 +153,19 @@ test "escapes invalid characters in url" do
       assert Path.basename(attachment_url["href"]) == "an%E2%80%A6%20image.jpg"
     end
 
-    test "replaces ? (question-mark) to %3f" do
+    test "replaces : (colon) and ? (question-mark) to %3A and %3F (respectively)" do
       File.cp!("test/fixtures/image.jpg", "test/fixtures/image_tmp.jpg")
 
       file = %Plug.Upload{
         content_type: "image/jpg",
         path: Path.absname("test/fixtures/image_tmp.jpg"),
-        filename: "an?image.jpg"
+        filename: "is:an?image.jpg"
       }
 
       {:ok, data} = Upload.store(file)
       [attachment_url | _] = data["url"]
 
-      assert Path.basename(attachment_url["href"]) == "an%3Fimage.jpg"
+      assert Path.basename(attachment_url["href"]) == "is%3Aan%3Fimage.jpg"
     end
   end
 end