diff --git a/lib/http.c b/lib/http.c
index f5709b68b..3618f8728 100644
--- a/lib/http.c
+++ b/lib/http.c
@@ -3982,7 +3982,14 @@ CURLcode Curl_http_readwrite_headers(struct Curl_easy *data,
#ifdef USE_ALTSVC
/* If enabled, the header is incoming and this is over HTTPS */
else if(data->asi && checkprefix("Alt-Svc:", k->p) &&
- (conn->handler->flags & PROTOPT_SSL)) {
+ ((conn->handler->flags & PROTOPT_SSL) ||
+#ifdef CURLDEBUG
+ /* allow debug builds to circumvent the HTTPS restriction */
+ getenv("CURL_ALTSVC_HTTP")
+#else
+ 0
+#endif
+ )) {
/* the ALPN of the current request */
enum alpnid id = (conn->httpversion == 20) ? ALPN_h2 : ALPN_h1;
result = Curl_altsvc_parse(data, data->asi,
diff --git a/tests/data/Makefile.inc b/tests/data/Makefile.inc
index bd24b4ba2..29e8c6924 100644
--- a/tests/data/Makefile.inc
+++ b/tests/data/Makefile.inc
@@ -60,7 +60,7 @@ test325 test326 test327 test328 test329 test330 \
\
test340 \
\
-test350 test351 test352 test353 test354 \
+test350 test351 test352 test353 test354 test355 test356 \
test393 test394 test395 \
\
test400 test401 test402 test403 test404 test405 test406 test407 test408 \
diff --git a/tests/data/test355 b/tests/data/test355
new file mode 100644
index 000000000..e9c4cb28f
--- /dev/null
+++ b/tests/data/test355
@@ -0,0 +1,57 @@
+
+
+
+HTTP
+Alt-Svc
+
+
+
+#
+# Server-side
+
+
+HTTP/1.1 200 OK
+Date: Thu, 09 Nov 2010 14:49:00 GMT
+Content-Length: 6
+Connection: close
+Content-Type: text/html
+Funny-head: yesyes
+
+-foo-
+
+
+
+#
+# Client-side
+
+
+alt-svc
+
+
+http
+
+
+load Alt-Svc from file and use
+
+
+http://%HOSTIP:%HTTPPORT/355 --alt-svc ""
+
+
+h1 example.com 80 h1 %HOSTIP %HTTPPORT "20290222 22:19:28" 0 0
+
+
+
+#
+# Verify data after the test has been "shot"
+
+
+^User-Agent:.*
+
+
+GET /355 HTTP/1.1
+Host: %HOSTIP:%HTTPPORT
+Accept: */*
+
+
+
+
diff --git a/tests/data/test356 b/tests/data/test356
new file mode 100644
index 000000000..26305f96a
--- /dev/null
+++ b/tests/data/test356
@@ -0,0 +1,69 @@
+
+
+
+HTTP
+Alt-Svc
+
+
+
+#
+# Server-side
+
+
+HTTP/1.1 200 OK
+Date: Thu, 09 Nov 2010 14:49:00 GMT
+Content-Length: 6
+Connection: close
+Content-Type: text/html
+Funny-head: yesyes
+Alt-Svc: h1="nowhere.foo:81"
+
+-foo-
+
+
+
+#
+# Client-side
+
+
+debug
+alt-svc
+
+
+http
+
+
+parse incoming Alt-Svc and save to file
+
+
+# make debug-curl accept Alt-Svc over plain HTTP
+CURL_ALTSVC_HTTP="yeah"
+
+http://%HOSTIP:%HTTPPORT/356 --alt-svc "log/altsvc-356"
+
+
+
+#
+# Verify data after the test has been "shot"
+
+
+^User-Agent:.*
+
+
+GET /356 HTTP/1.1
+Host: %HOSTIP:%HTTPPORT
+Accept: */*
+
+
+
+# strip out the (dynamic) expire date from the file so that the rest
+# matches
+s/\"([^\"]*)\"/TIMESTAMP/
+
+
+# Your alt-svc cache. https://curl.haxx.se/docs/alt-svc.html
+# This file was generated by libcurl! Edit at your own risk.
+h1 %HOSTIP %HTTPPORT h1 nowhere.foo 81 TIMESTAMP 0 0
+
+
+