diff --git a/main/SAPI.c b/main/SAPI.c
index 2e697f9779669..a2bd456d9baf6 100644
--- a/main/SAPI.c
+++ b/main/SAPI.c
@@ -371,7 +371,7 @@ SAPI_API size_t sapi_apply_default_charset(char **mimetype, size_t len)
 	charset = SG(default_charset) ? SG(default_charset) : SAPI_DEFAULT_CHARSET;
 
 	if (*mimetype != NULL) {
-		if (*charset && strncmp(*mimetype, "text/", 5) == 0 && strstr(*mimetype, "charset=") == NULL) {
+		if (*charset && strncmp(*mimetype, "text/", 5) == 0 && strstr(*mimetype, "charset=") == NULL && strcmp(*mimetype, "text/event-stream") != 0) {
 			newlen = len + (sizeof(";charset=")-1) + strlen(charset);
 			newtype = emalloc(newlen + 1);
 	 		PHP_STRLCPY(newtype, *mimetype, newlen + 1, len);
diff --git a/sapi/cli/tests/gh11146.phpt b/sapi/cli/tests/gh11146.phpt
new file mode 100644
index 0000000000000..20edbcec1a1ca
--- /dev/null
+++ b/sapi/cli/tests/gh11146.phpt
@@ -0,0 +1,45 @@
+--TEST--
+GH-11146: The built-in webserver will add ";charset=UTF-8" to the end of the Content-Type response header of the SSE response.
+--SKIPIF--
+<?php
+include "skipif.inc";
+?>
+--FILE--
+<?php
+include "php_cli_server.inc";
+php_cli_server_start(
+    <<<'CODE'
+header('Content-Type: text/event-stream');
+for ($i = 0; $i < 3; ++$i) {
+    echo 'data: ' . $i . "\n\n";
+}
+CODE
+);
+
+$host = PHP_CLI_SERVER_HOSTNAME;
+
+$fp = php_cli_server_connect();
+if(fwrite($fp, <<<HEADER
+GET / HTTP/1.1
+Host: {$host}
+
+
+HEADER)) {
+    while (!feof($fp)) {
+        echo fgets($fp);
+    }
+}
+?>
+--EXPECTF--
+HTTP/1.1 200 OK
+Host: %s
+Date: %s
+Connection: close
+X-Powered-By: PHP/%s
+Content-Type: text/event-stream
+
+data: 0
+
+data: 1
+
+data: 2