diff --git a/swh/deposit/file_storage.py b/swh/deposit/file_storage.py
new file mode 100644
--- /dev/null
+++ b/swh/deposit/file_storage.py
@@ -0,0 +1,84 @@
+# Copyright (C) 2020  The Software Heritage developers
+# Copyright (c) Django Software Foundation and individual contributors.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+#     1. Redistributions of source code must retain the above copyright notice,
+#        this list of conditions and the following disclaimer.
+#
+#     2. Redistributions in binary form must reproduce the above copyright
+#        notice, this list of conditions and the following disclaimer in the
+#        documentation and/or other materials provided with the distribution.
+#
+#     3. Neither the name of Django nor the names of its contributors may be used
+#        to endorse or promote products derived from this software without
+#        specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+import os.path
+
+from django.core.exceptions import SuspiciousFileOperation
+from django.core.files.storage import FileSystemStorage
+from django.utils.crypto import get_random_string
+
+
+class PrefixedFileSystemStorage(FileSystemStorage):
+    """Subclass of FileSystemStorage, that disambiguates by adding
+    a random prefix, instead of a random suffix.
+    This prevents issues with compound extensions (eg. .tar.gz), as a suffix
+    changes the second-to-last extension; which messages with shutil's
+    file type detection.."""
+
+    # This function is copy-pasted from
+    # <https://github.com/django/django/blob/98ef3829e96ebc73d4d446f92465e671ff520d2b/django/core/files/storage.py#L63-L92>
+    # with just the two computations of 'name' changed
+    #
+    # TODO: when we upgrade to Django 3, this whole function can be removed
+    # and replaced with an override of get_alternative_name.
+    def get_available_name(self, name, max_length=None):
+        """
+        Return a filename that's free on the target storage system and
+        available for new content to be written to.
+        """
+        dir_name, file_name = os.path.split(name)
+        file_root, file_ext = os.path.splitext(file_name)
+        # If the filename already exists, add an underscore and a random 7
+        # character alphanumeric string (before the file extension, if one
+        # exists) to the filename until the generated filename doesn't exist.
+        # Truncate original name if required, so the new filename does not
+        # exceed the max_length.
+        while self.exists(name) or (max_length and len(name) > max_length):
+            # file_ext includes the dot.
+            name = os.path.join(
+                dir_name, "%s_%s%s" % (get_random_string(7), file_root, file_ext)
+            )
+            if max_length is None:
+                continue
+            # Truncate file_root if max_length exceeded.
+            truncation = len(name) - max_length
+            if truncation > 0:
+                file_root = file_root[:-truncation]
+                # Entire file_root was truncated in attempt to find an available
+                # filename.
+                if not file_root:
+                    raise SuspiciousFileOperation(
+                        'Storage can not find an available filename for "%s". '
+                        "Please make sure that the corresponding file field "
+                        'allows sufficient "max_length".' % name
+                    )
+                name = os.path.join(
+                    dir_name, "%s_%s%s" % (get_random_string(7), file_root, file_ext)
+                )
+        return name
diff --git a/swh/deposit/settings/common.py b/swh/deposit/settings/common.py
--- a/swh/deposit/settings/common.py
+++ b/swh/deposit/settings/common.py
@@ -112,3 +112,5 @@
     "django.core.files.uploadhandler.MemoryFileUploadHandler",
     "django.core.files.uploadhandler.TemporaryFileUploadHandler",
 ]
+
+DEFAULT_FILE_STORAGE = "swh.deposit.file_storage.PrefixedFileSystemStorage"
diff --git a/swh/deposit/tests/common.py b/swh/deposit/tests/common.py
--- a/swh/deposit/tests/common.py
+++ b/swh/deposit/tests/common.py
@@ -133,9 +133,5 @@
             archive_name_to_check
 
     """
-    if "." in archive_name:
-        filename, extension = archive_name.split(".")
-        pattern = re.compile(".*/%s.*\\.%s" % (filename, extension))
-    else:
-        pattern = re.compile(".*/%s" % archive_name)
+    pattern = re.compile(".*/.*_%s" % archive_name)
     assert pattern.match(archive_name_to_check) is not None