"And please note: You need to upgrade apt-transport-https for testing, just apt does nothing." Aha, I might have forgotten to upgrade apt-transport-https... But, I just tested, and now I'm getting: estan@newton:~$ /usr/lib/apt/apt-helper download-file http://downloads.sourceforge.net/corefonts/andale32.exe test.exe Err:1 http://downloads.sourceforge.net/corefonts/andale32.exe The HTTP server sent an invalid Content-Range header E: Failed to fetch https://netassist.dl.sourceforge.net/project/corefonts/the fonts/final/andale32.exe The HTTP server sent an invalid Content-Range header E: Download Failed estan@newton:~$ /usr/lib/apt/apt-helper download-file http://downloads.sourceforge.net/corefonts/andale32.exe test.exe Err:1 http://downloads.sourceforge.net/corefonts/andale32.exe The HTTP server sent an invalid Content-Range header E: Failed to fetch https://netcologne.dl.sourceforge.net/project/corefonts/the fonts/final/andale32.exe The HTTP server sent an invalid Content-Range header E: Download Failed estan@newton:~$ /usr/lib/apt/apt-helper download-file http://downloads.sourceforge.net/corefonts/andale32.exe test.exe Err:1 http://downloads.sourceforge.net/corefonts/andale32.exe The HTTP server sent an invalid Content-Range header E: Failed to fetch https://netcologne.dl.sourceforge.net/project/corefonts/the fonts/final/andale32.exe The HTTP server sent an invalid Content-Range header E: Download Failed estan@newton:~$ apt-cache policy apt apt-transport-https apt: Installed: 1.2.19 Candidate: 1.2.19 Version table: *** 1.2.19 500 500 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages 100 /var/lib/dpkg/status 1.2.18 500 500 http://se.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages 1.2.15ubuntu0.2 500 500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages 1.2.10ubuntu1 500 500 http://se.archive.ubuntu.com/ubuntu xenial/main amd64 Packages apt-transport-https: Installed: 1.2.19 Candidate: 1.2.19 Version table: *** 1.2.19 500 500 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages 100 /var/lib/dpkg/status 1.2.18 500 500 http://se.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages 1.2.15ubuntu0.2 500 500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages 1.2.10ubuntu1 500 500 http://se.archive.ubuntu.com/ubuntu xenial/main amd64 Packages estan@newton:~$ With debug output, I first got: estan@newton:~$ /usr/lib/apt/apt-helper -o debug::acquire::https=1 -o debug::acquire::http=1 download-file http://downloads.sourceforge.net/corefonts/andale32.exe test.exe 0% [Working]GET /corefonts/andale32.exe HTTP/1.1 Host: downloads.sourceforge.net Range: bytes=198384- If-Range: Thu, 15 Aug 2002 14:33:49 GMT User-Agent: Debian APT-HTTP/1.3 (1.2.19) Answer for: http://downloads.sourceforge.net/corefonts/andale32.exe HTTP/1.1 301 Moved Permanently Server: nginx Date: Wed, 18 Jan 2017 18:30:14 GMT Content-Type: text/html; charset=UTF-8 Connection: close Location: http://downloads.sourceforge.net/project/corefonts/the%20fonts/final/andale32.exe Content-Length: 178 0% [Working]GET /project/corefonts/the%20fonts/final/andale32.exe HTTP/1.1 Host: downloads.sourceforge.net Range: bytes=198384- If-Range: Thu, 15 Aug 2002 14:33:49 GMT User-Agent: Debian APT-HTTP/1.3 (1.2.19) GET /project/corefonts/the%20fonts/final/andale32.exe HTTP/1.1 Host: downloads.sourceforge.net Range: bytes=198384- If-Range: Thu, 15 Aug 2002 14:33:49 GMT User-Agent: Debian APT-HTTP/1.3 (1.2.19) Answer for: http://downloads.sourceforge.net/project/corefonts/the fonts/final/andale32.exe HTTP/1.1 302 Found Server: nginx Date: Wed, 18 Jan 2017 18:30:14 GMT Content-Type: text/html; charset=UTF-8 Connection: close content-disposition: attachment; filename="andale32.exe" Set-Cookie: sf_mirror_attempt="corefonts:vorboss:the%20fonts/final/andale32.exe"; expires=120; Path=/ Location: https://vorboss.dl.sourceforge.net/project/corefonts/the%20fonts/final/andale32.exe Content-Length: 163 0% [Working]* Trying 5.10.152.194... * Connected to vorboss.dl.sourceforge.net (5.10.152.194) port 443 (#0) * found 174 certificates in /etc/ssl/certs/ca-certificates.crt * found 708 certificates in /etc/ssl/certs * ALPN, offering http/1.1 0% [Working]* SSL connection using TLS1.2 / ECDHE_RSA_AES_128_GCM_SHA256 * server certificate verification OK * server certificate status verification SKIPPED * common name: vorboss.dl.sourceforge.net (matched) * server certificate expiration date OK * server certificate activation date OK * certificate public key: RSA * certificate version: #3 * subject: CN=vorboss.dl.sourceforge.net * start date: Mon, 31 Oct 2016 19:27:00 GMT * expire date: Sun, 29 Jan 2017 19:27:00 GMT * issuer: C=US,O=Let's Encrypt,CN=Let's Encrypt Authority X3 * compression: NULL * ALPN, server did not agree to a protocol > GET /project/corefonts/the%20fonts/final/andale32.exe HTTP/1.1 Host: vorboss.dl.sourceforge.net User-Agent: Debian APT-CURL/1.0 (1.2.19) Accept: */* Cache-Control: max-age=0 Range: bytes=198384- If-Range: Thu, 15 Aug 2002 14:33:49 GMT < HTTP/1.1 302 Found < Date: Wed, 18 Jan 2017 18:30:24 GMT < Server: Apache/2.2.22 (Debian) < Location: http://downloads.sourceforge.net/mirrorproblem?failedmirror=vorboss.dl.sourceforge.net < Vary: Accept-Encoding < Connection: close < Transfer-Encoding: chunked < Content-Type: text/html; charset=iso-8859-1 < * Closing connection 0 * Issue another request to this URL: 'http://downloads.sourceforge.net/mirrorproblem?failedmirror=vorboss.dl.sourceforge.net' * Protocol "http" not supported or disabled in libcurl * Closing connection -1 Err:1 http://downloads.sourceforge.net/corefonts/andale32.exe Protocol "http" not supported or disabled in libcurl E: Failed to fetch https://vorboss.dl.sourceforge.net/project/corefonts/the fonts/final/andale32.exe Protocol "http" not supported or disabled in libcurl E: Download Failed estan@newton:~$ But then I tried again and got: estan@newton:~$ /usr/lib/apt/apt-helper -o debug::acquire::https=1 -o debug::acquire::http=1 download-file http://downloads.sourceforge.net/corefonts/andale32.exe test.exe 0% [Working]GET /corefonts/andale32.exe HTTP/1.1 Host: downloads.sourceforge.net Range: bytes=198384- If-Range: Thu, 15 Aug 2002 14:33:49 GMT User-Agent: Debian APT-HTTP/1.3 (1.2.19) Answer for: http://downloads.sourceforge.net/corefonts/andale32.exe HTTP/1.1 301 Moved Permanently Server: nginx Date: Wed, 18 Jan 2017 18:30:54 GMT Content-Type: text/html; charset=UTF-8 Connection: close Location: http://downloads.sourceforge.net/project/corefonts/the%20fonts/final/andale32.exe Content-Length: 178 0% [Working]GET /project/corefonts/the%20fonts/final/andale32.exe HTTP/1.1 Host: downloads.sourceforge.net Range: bytes=198384- If-Range: Thu, 15 Aug 2002 14:33:49 GMT User-Agent: Debian APT-HTTP/1.3 (1.2.19) GET /project/corefonts/the%20fonts/final/andale32.exe HTTP/1.1 Host: downloads.sourceforge.net Range: bytes=198384- If-Range: Thu, 15 Aug 2002 14:33:49 GMT User-Agent: Debian APT-HTTP/1.3 (1.2.19) Answer for: http://downloads.sourceforge.net/project/corefonts/the fonts/final/andale32.exe HTTP/1.1 302 Found Server: nginx Date: Wed, 18 Jan 2017 18:30:54 GMT Content-Type: text/html; charset=UTF-8 Connection: close content-disposition: attachment; filename="andale32.exe" Set-Cookie: sf_mirror_attempt="corefonts:netassist:the%20fonts/final/andale32.exe"; expires=120; Path=/ Location: https://netassist.dl.sourceforge.net/project/corefonts/the%20fonts/final/andale32.exe Content-Length: 165 0% [Working]* Trying 62.205.134.42... * Connected to netassist.dl.sourceforge.net (62.205.134.42) port 443 (#0) * found 174 certificates in /etc/ssl/certs/ca-certificates.crt * found 708 certificates in /etc/ssl/certs * ALPN, offering http/1.1 0% [Working]* SSL connection using TLS1.2 / ECDHE_RSA_AES_256_GCM_SHA384 * server certificate verification OK * server certificate status verification SKIPPED * common name: netassist.dl.sourceforge.net (matched) * server certificate expiration date OK * server certificate activation date OK * certificate public key: RSA * certificate version: #3 * subject: CN=netassist.dl.sourceforge.net * start date: Thu, 05 Jan 2017 23:28:00 GMT * expire date: Wed, 05 Apr 2017 23:28:00 GMT * issuer: C=US,O=Let's Encrypt,CN=Let's Encrypt Authority X3 * compression: NULL * ALPN, server did not agree to a protocol > GET /project/corefonts/the%20fonts/final/andale32.exe HTTP/1.1 Host: netassist.dl.sourceforge.net User-Agent: Debian APT-CURL/1.0 (1.2.19) Accept: */* Cache-Control: max-age=0 Range: bytes=198384- If-Range: Thu, 15 Aug 2002 14:33:49 GMT 0% [Working]< HTTP/1.1 302 Moved Temporarily < Server: nginx < Date: Wed, 18 Jan 2017 18:50:58 GMT < Content-Type: text/html < Content-Length: 154 < Connection: close < Content-Range: bytes */198384 * Failed writing header * Closing connection 0 Err:1 http://downloads.sourceforge.net/corefonts/andale32.exe The HTTP server sent an invalid Content-Range header E: Failed to fetch https://netassist.dl.sourceforge.net/project/corefonts/the fonts/final/andale32.exe The HTTP server sent an invalid Content-Range header E: Download Failed estan@newton:~$