diff --git a/qutebrowser/browser/commands.py b/qutebrowser/browser/commands.py
index 2f5f617fe..a2cdbdbbe 100644
--- a/qutebrowser/browser/commands.py
+++ b/qutebrowser/browser/commands.py
@@ -1334,6 +1334,9 @@ class CommandDispatcher:
                                       scope='window', window=self._win_id)
         target = None
         if dest is not None:
+            dest = downloads.transform_path(dest)
+            if dest is None:
+                raise cmdexc.CommandError("Invalid target filename")
             target = downloads.FileDownloadTarget(dest)
 
         tab = self._current_widget()
diff --git a/qutebrowser/browser/downloads.py b/qutebrowser/browser/downloads.py
index 51ccdbfeb..f9b246d3a 100644
--- a/qutebrowser/browser/downloads.py
+++ b/qutebrowser/browser/downloads.py
@@ -19,11 +19,13 @@
 
 """Shared QtWebKit/QtWebEngine code for downloads."""
 
+import re
 import sys
 import html
 import os.path
 import collections
 import functools
+import pathlib
 import tempfile
 
 import sip
@@ -161,6 +163,25 @@ def get_filename_question(*, suggested_filename, url, parent=None):
     return q
 
 
+def transform_path(path):
+    r"""Do platform-specific transformations, like changing E: to E:\.
+
+    Returns None if the path is invalid on the current platform.
+    """
+    if sys.platform != "win32":
+        return path
+    path = utils.expand_windows_drive(path)
+    # Drive dependent working directories are not supported, e.g.
+    # E:filename is invalid
+    if re.match(r'[A-Z]:[^\\]', path, re.IGNORECASE):
+        return None
+    # Paths like COM1, ...
+    # See https://github.com/qutebrowser/qutebrowser/issues/82
+    if pathlib.Path(path).is_reserved():
+        return None
+    return path
+
+
 class NoFilenameError(Exception):
 
     """Raised when we can't find out a filename in DownloadTarget."""
diff --git a/qutebrowser/mainwindow/prompt.py b/qutebrowser/mainwindow/prompt.py
index 2f833c3a3..b50bcb323 100644
--- a/qutebrowser/mainwindow/prompt.py
+++ b/qutebrowser/mainwindow/prompt.py
@@ -19,11 +19,9 @@
 
 """Showing prompts above the statusbar."""
 
-import re
 import sys
 import os.path
 import html
-import pathlib
 import collections
 
 import sip
@@ -646,31 +644,13 @@ class FilenamePrompt(_BasePrompt):
         self._file_model.directoryLoaded.connect(
             lambda: self._file_model.sort(0))
 
-    def _transform_path(self, path):
-        r"""Do platform-specific transformations, like changing E: to E:\.
-
-        Returns None if the path is invalid on the current platform.
-        """
-        if sys.platform != "win32":
-            return path
-        path = utils.expand_windows_drive(path)
-        # Drive dependent working directories are not supported, e.g.
-        # E:filename is invalid
-        if re.match(r'[A-Z]:[^\\]', path, re.IGNORECASE):
-            return None
-        # Paths like COM1, ...
-        # See https://github.com/qutebrowser/qutebrowser/issues/82
-        if pathlib.Path(path).is_reserved():
-            return None
-        return path
-
     def _show_error(self, msg):
         log.prompt.error(msg)
         QToolTip.showText(self._lineedit.mapToGlobal(QPoint(0, 0)), msg)
 
     def accept(self, value=None):
         text = value if value is not None else self._lineedit.text()
-        text = self._transform_path(text)
+        text = downloads.transform_path(text)
         if text is None:
             self._show_error("Invalid filename")
             return False
@@ -725,7 +705,7 @@ class DownloadFilenamePrompt(FilenamePrompt):
 
     def accept(self, value=None):
         text = value if value is not None else self._lineedit.text()
-        text = self._transform_path(text)
+        text = downloads.transform_path(text)
         if text is None:
             self._show_error("Invalid filename")
             return False
diff --git a/tests/end2end/features/downloads.feature b/tests/end2end/features/downloads.feature
index b47edf8d8..38c4cc627 100644
--- a/tests/end2end/features/downloads.feature
+++ b/tests/end2end/features/downloads.feature
@@ -140,6 +140,16 @@ Feature: Downloading things from a website.
         And I run :prompt-cancel
         Then "Invalid filename" should be logged
 
+    @windows
+    Scenario: Downloading a file to a reserved path with :download
+        When I run :download data/downloads/download.bin --dest=COM1
+        Then the error "Invalid target filename" should be shown
+
+    @windows
+    Scenario: Download a file to a drive-relative working directory with :download
+        When I run :download data/downloads/download.bin --dest=C:foobar
+        Then the error "Invalid target filename" should be shown
+
     ## :download-retry
 
     Scenario: Retrying a failed download