diff --git a/web/packages/core/src/ruffle-player.js b/web/packages/core/src/ruffle-player.js
index 97030cac8..272894c4b 100644
--- a/web/packages/core/src/ruffle-player.js
+++ b/web/packages/core/src/ruffle-player.js
@@ -172,7 +172,7 @@ exports.RufflePlayer = class RufflePlayer extends HTMLElement {
      * @param {URLSearchParams|String|Object} [parameters] The parameters (also known as "flashvars") to load the movie with.
      * If it's a string, it will be decoded into an object.
      * If it's an object, every key and value must be a String.
-     * If it's null or undefined, it will attempt to be parsed from the URL. If you explicitly want no flashvars, use {}.
+     * These parameters will be merged onto any found in the query portion of the swf URL.
      */
     async stream_swf_url(url, parameters) {
         //TODO: Actually stream files...
@@ -181,13 +181,11 @@ exports.RufflePlayer = class RufflePlayer extends HTMLElement {
                 console.log("Loading SWF file " + url);
 
                 await this.ensure_fresh_instance();
-                if (
-                    (parameters === null || parameters === undefined) &&
-                    url.indexOf("?") > -1
-                ) {
-                    parameters = url.substring(url.indexOf("?"));
-                }
-                this.instance.stream_from(url, sanitize_parameters(parameters));
+                parameters = {
+                    ...sanitize_parameters(url.substring(url.indexOf("?"))),
+                    ...sanitize_parameters(parameters),
+                };
+                this.instance.stream_from(url, parameters);
 
                 if (this.play_button) {
                     this.play_button.style.display = "block";
diff --git a/web/packages/selfhosted/test/polyfill/object_flashvars/expected.html b/web/packages/selfhosted/test/polyfill/object_flashvars/expected.html
index cec2c2beb..d034e9b05 100644
--- a/web/packages/selfhosted/test/polyfill/object_flashvars/expected.html
+++ b/web/packages/selfhosted/test/polyfill/object_flashvars/expected.html
@@ -1,19 +1,20 @@
 <ruffle-object
-    type="application/x-shockwave-flash"
-    classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000"
-    width="550"
-    height="400"
-    codebase="http://fpdownload.adobe.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,0,0"
->
-    <param name="movie" value="/test_assets/flashvars.swf?a=1&b=3+%253&c&d[]=foo" />
-    <param name="quality" value="high" />
-    <param name="menu" value="false" />
-    <ruffle-embed
-        src="/test_assets/flashvars.swf?a=1&b=3+%253&c&d[]=foo"
+        type="application/x-shockwave-flash"
+        classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000"
         width="550"
         height="400"
-        quality="high"
-        menu="false"
-        pluginspage="http://www.adobe.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash"
+        codebase="http://fpdownload.adobe.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,0,0"
+>
+    <param name="movie" value="/test_assets/flashvars.swf?a=default&c" />
+    <param name="quality" value="high" />
+    <param name="menu" value="false" />
+    <param name="flashvars" value="a=1&b=3+%253&d[]=foo" />
+    <ruffle-embed
+            src="/test_assets/flashvars.swf?a=default&c"
+            width="550"
+            height="400"
+            quality="high"
+            menu="false"
+            pluginspage="http://www.adobe.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash"
     />
 </ruffle-object>
\ No newline at end of file
diff --git a/web/packages/selfhosted/test/polyfill/object_flashvars/index.html b/web/packages/selfhosted/test/polyfill/object_flashvars/index.html
index b1943a5ae..c37d73359 100644
--- a/web/packages/selfhosted/test/polyfill/object_flashvars/index.html
+++ b/web/packages/selfhosted/test/polyfill/object_flashvars/index.html
@@ -14,11 +14,12 @@
                 height="400"
                 codebase="http://fpdownload.adobe.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,0,0"
             >
-                <param name="movie" value="/test_assets/flashvars.swf?a=1&b=3+%253&c&d[]=foo" />
+                <param name="movie" value="/test_assets/flashvars.swf?a=default&c" />
                 <param name="quality" value="high" />
                 <param name="menu" value="false" />
+                <param name="flashvars" value="a=1&b=3+%253&d[]=foo" />
                 <embed
-                    src="/test_assets/flashvars.swf?a=1&b=3+%253&c&d[]=foo"
+                    src="/test_assets/flashvars.swf?a=default&c"
                     width="550"
                     height="400"
                     quality="high"
diff --git a/web/packages/selfhosted/test/polyfill/object_flashvars_in_url/expected.html b/web/packages/selfhosted/test/polyfill/object_flashvars_in_url/expected.html
index 5487b30ed..073a2d70b 100644
--- a/web/packages/selfhosted/test/polyfill/object_flashvars_in_url/expected.html
+++ b/web/packages/selfhosted/test/polyfill/object_flashvars_in_url/expected.html
@@ -1,20 +1,19 @@
 <ruffle-object
-    type="application/x-shockwave-flash"
-    classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000"
-    width="550"
-    height="400"
-    codebase="http://fpdownload.adobe.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,0,0"
->
-    <param name="movie" value="/test_assets/flashvars.swf" />
-    <param name="quality" value="high" />
-    <param name="menu" value="false" />
-    <param name="flashvars" value="a=1&b=3+%253&c&d[]=foo" />
-    <ruffle-embed
-        src="/test_assets/flashvars.swf"
+        type="application/x-shockwave-flash"
+        classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000"
         width="550"
         height="400"
-        quality="high"
-        menu="false"
-        pluginspage="http://www.adobe.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash"
+        codebase="http://fpdownload.adobe.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,0,0"
+>
+    <param name="movie" value="/test_assets/flashvars.swf?a=1&b=3+%253&c&d[]=foo" />
+    <param name="quality" value="high" />
+    <param name="menu" value="false" />
+    <ruffle-embed
+            src="/test_assets/flashvars.swf?a=1&b=3+%253&c&d[]=foo"
+            width="550"
+            height="400"
+            quality="high"
+            menu="false"
+            pluginspage="http://www.adobe.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash"
     />
 </ruffle-object>
\ No newline at end of file
diff --git a/web/packages/selfhosted/test/polyfill/object_flashvars_in_url/index.html b/web/packages/selfhosted/test/polyfill/object_flashvars_in_url/index.html
index 2606a0c40..b1943a5ae 100644
--- a/web/packages/selfhosted/test/polyfill/object_flashvars_in_url/index.html
+++ b/web/packages/selfhosted/test/polyfill/object_flashvars_in_url/index.html
@@ -14,12 +14,11 @@
                 height="400"
                 codebase="http://fpdownload.adobe.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,0,0"
             >
-                <param name="movie" value="/test_assets/flashvars.swf" />
+                <param name="movie" value="/test_assets/flashvars.swf?a=1&b=3+%253&c&d[]=foo" />
                 <param name="quality" value="high" />
                 <param name="menu" value="false" />
-                <param name="flashvars" value="a=1&b=3+%253&c&d[]=foo" />
                 <embed
-                    src="/test_assets/flashvars.swf"
+                    src="/test_assets/flashvars.swf?a=1&b=3+%253&c&d[]=foo"
                     width="550"
                     height="400"
                     quality="high"