diff --git a/http.c b/http.c
index 412f7af250..ea9b16861b 100644
--- a/http.c
+++ b/http.c
@@ -761,6 +761,69 @@ static int has_proxy_cert_password(void)
 	return 1;
 }
 
+static const struct socks_proxy_type {
+	const char *name;
+	long curlsym;
+} socks_proxy_types[] = {
+	{ "socks", CURLPROXY_SOCKS4 },
+	{ "socks4", CURLPROXY_SOCKS4 },
+	{ "socks4a", CURLPROXY_SOCKS4A },
+	{ "socks5", CURLPROXY_SOCKS5 },
+	{ "socks5h", CURLPROXY_SOCKS5_HOSTNAME },
+};
+
+static const struct socks_proxy_type *find_socks_proxy_type(const char *protocol)
+{
+	int i;
+
+	if (!protocol)
+		return NULL;
+
+	for (i = 0; i < ARRAY_SIZE(socks_proxy_types); i++) {
+		if (!strcmp(socks_proxy_types[i].name, protocol))
+			return &socks_proxy_types[i];
+	}
+
+	return NULL;
+}
+
+static int is_socks_proxy_protocol(const char *protocol)
+{
+	return !!find_socks_proxy_type(protocol);
+}
+
+static int set_curl_proxy_type(CURL *result, const char *protocol)
+{
+	const struct socks_proxy_type *socks_proxy_type;
+
+	if (!protocol || !strcmp(protocol, "http"))
+		return 0;
+
+	socks_proxy_type = find_socks_proxy_type(protocol);
+	if (socks_proxy_type) {
+		curl_easy_setopt(result, CURLOPT_PROXYTYPE, socks_proxy_type->curlsym);
+		return 0;
+	}
+
+	if (!strcmp(protocol, "https")) {
+		curl_easy_setopt(result, CURLOPT_PROXYTYPE, (long)CURLPROXY_HTTPS);
+
+		if (http_proxy_ssl_cert)
+			curl_easy_setopt(result, CURLOPT_PROXY_SSLCERT,
+					 http_proxy_ssl_cert);
+
+		if (http_proxy_ssl_key)
+			curl_easy_setopt(result, CURLOPT_PROXY_SSLKEY,
+					 http_proxy_ssl_key);
+
+		if (has_proxy_cert_password())
+			curl_easy_setopt(result, CURLOPT_PROXY_KEYPASSWD,
+					 proxy_cert_auth.password);
+	}
+
+	return -1;
+}
+
 /* Return 1 if redactions have been made, 0 otherwise. */
 static int redact_sensitive_header(struct strbuf *header, size_t offset)
 {
@@ -1231,30 +1294,6 @@ static CURL *get_curl_handle(void)
 	} else if (curl_http_proxy) {
 		struct strbuf proxy = STRBUF_INIT;
 
-		if (starts_with(curl_http_proxy, "socks5h"))
-			curl_easy_setopt(result,
-				CURLOPT_PROXYTYPE, (long)CURLPROXY_SOCKS5_HOSTNAME);
-		else if (starts_with(curl_http_proxy, "socks5"))
-			curl_easy_setopt(result,
-				CURLOPT_PROXYTYPE, (long)CURLPROXY_SOCKS5);
-		else if (starts_with(curl_http_proxy, "socks4a"))
-			curl_easy_setopt(result,
-				CURLOPT_PROXYTYPE, (long)CURLPROXY_SOCKS4A);
-		else if (starts_with(curl_http_proxy, "socks"))
-			curl_easy_setopt(result,
-				CURLOPT_PROXYTYPE, (long)CURLPROXY_SOCKS4);
-		else if (starts_with(curl_http_proxy, "https")) {
-			curl_easy_setopt(result, CURLOPT_PROXYTYPE, (long)CURLPROXY_HTTPS);
-
-			if (http_proxy_ssl_cert)
-				curl_easy_setopt(result, CURLOPT_PROXY_SSLCERT, http_proxy_ssl_cert);
-
-			if (http_proxy_ssl_key)
-				curl_easy_setopt(result, CURLOPT_PROXY_SSLKEY, http_proxy_ssl_key);
-
-			if (has_proxy_cert_password())
-				curl_easy_setopt(result, CURLOPT_PROXY_KEYPASSWD, proxy_cert_auth.password);
-		}
 		if (strstr(curl_http_proxy, "://"))
 			credential_from_url(&proxy_auth, curl_http_proxy);
 		else {
@@ -1264,6 +1303,10 @@ static CURL *get_curl_handle(void)
 			strbuf_release(&url);
 		}
 
+		if (set_curl_proxy_type(result, proxy_auth.protocol) < 0)
+			die("Invalid proxy URL '%s': unsupported proxy scheme '%s'",
+			    curl_http_proxy, proxy_auth.protocol);
+
 		if (!proxy_auth.host)
 			die("Invalid proxy URL '%s'", curl_http_proxy);
 
@@ -1274,7 +1317,7 @@ static CURL *get_curl_handle(void)
 			if (ver->version_num < 0x075400)
 				die("libcurl 7.84 or later is required to support paths in proxy URLs");
 
-			if (!starts_with(proxy_auth.protocol, "socks"))
+			if (!is_socks_proxy_protocol(proxy_auth.protocol))
 				die("Invalid proxy URL '%s': only SOCKS proxies support paths",
 				    curl_http_proxy);
 
diff --git a/t/t5564-http-proxy.sh b/t/t5564-http-proxy.sh
index b4d95b12ca..817cd1f984 100755
--- a/t/t5564-http-proxy.sh
+++ b/t/t5564-http-proxy.sh
@@ -102,4 +102,10 @@ test_expect_success 'Unix socket requires localhost' - <<\EOT
 	}
 EOT
 
+test_expect_success 'unknown proxy scheme is rejected' '
+	test_must_fail git clone -c http.proxy=htpp://127.0.0.1 \
+		https://example.com/repo.git 2>err &&
+	test_grep "unsupported proxy scheme '\''htpp'\''" err
+'
+
 test_done