diff --git a/includes/Hooks.php b/includes/Hooks.php
index e48dd4c8..e66150b3 100644
--- a/includes/Hooks.php
+++ b/includes/Hooks.php
@@ -223,7 +223,7 @@ class Hooks implements
 			$parserError = htmlspecialchars( $e->getMessage() );
 
 			// #iferror-compatible error element
-			return "<strong class=\"error\"><span class=\"scribunto-error\" id=\"$id\">" .
+			return "<strong class=\"error\"><span class=\"scribunto-error $id\">" .
 				$parserError . "</span></strong>";
 		}
 	}
diff --git a/modules/ext.scribunto.errors.js b/modules/ext.scribunto.errors.js
index 7330ac3e..12a9bcc3 100644
--- a/modules/ext.scribunto.errors.js
+++ b/modules/ext.scribunto.errors.js
@@ -1,11 +1,15 @@
 ( () => {
 
 	mw.hook( 'wikipage.content' ).add( () => {
-		const regex = /^mw-scribunto-error-(\w+)/;
+		const regex = /\bmw-scribunto-error-(\w+)\b/;
 		let popup;
 
 		$( '.scribunto-error' ).each( ( index, span ) => {
-			const matches = regex.exec( span.id );
+			let matches = regex.exec( span.className );
+			if ( matches === null ) {
+				// T375539: backward-compatibility with old cached HTML
+				matches = regex.exec( span.id );
+			}
 			if ( matches === null ) {
 				mw.log( 'mw.scribunto.errors: regex mismatch!' );
 				return;
diff --git a/tests/parser/luaParserTests.txt b/tests/parser/luaParserTests.txt
index 108fec31..20c6916c 100644
--- a/tests/parser/luaParserTests.txt
+++ b/tests/parser/luaParserTests.txt
@@ -272,10 +272,10 @@ extension=ScribuntoErrors-5e10d413
 cat=Pages_with_script_errors sort=
 extension[ScribuntoErrors-5e10d413]="<p>Script error: No such module \"foo\".</p><p>No further details are available.</p>"
 !! html/php
-<p><strong class="error"><span class="scribunto-error" id="mw-scribunto-error-5e10d413">Script error: No such module &quot;foo&quot;.</span></strong>
+<p><strong class="error"><span class="scribunto-error mw-scribunto-error-5e10d413">Script error: No such module &quot;foo&quot;.</span></strong>
 </p>
 !! html/parsoid
-<p><strong class="error" about="#mwt1" typeof="mw:Transclusion" data-mw='{"parts":[{"template":{"target":{"wt":"#invoke:foo","function":"invoke"},"params":{"1":{"wt":"bar"}},"i":0}}]}'><span class="scribunto-error" id="mw-scribunto-error-5e10d413">Script error: No such module <span typeof="mw:Entity">"</span>foo<span typeof="mw:Entity">"</span>.</span></strong></p>
+<p><strong class="error" about="#mwt1" typeof="mw:Transclusion" data-mw='{"parts":[{"template":{"target":{"wt":"#invoke:foo","function":"invoke"},"params":{"1":{"wt":"bar"}},"i":0}}]}'><span class="scribunto-error mw-scribunto-error-5e10d413">Script error: No such module <span typeof="mw:Entity">"</span>foo<span typeof="mw:Entity">"</span>.</span></strong></p>
 !! end
 
 !! test
@@ -290,10 +290,10 @@ extension=ScribuntoErrors-d64a22ba
 cat=Pages_with_script_errors sort=
 extension[ScribuntoErrors-d64a22ba]="<p>Script error: The function \"blah\" does not exist.</p><p>No further details are available.</p>"
 !! html/php
-<p><strong class="error"><span class="scribunto-error" id="mw-scribunto-error-d64a22ba">Script error: The function &quot;blah&quot; does not exist.</span></strong>
+<p><strong class="error"><span class="scribunto-error mw-scribunto-error-d64a22ba">Script error: The function &quot;blah&quot; does not exist.</span></strong>
 </p>
 !! html/parsoid
-<p><strong class="error" about="#mwt1" typeof="mw:Transclusion" data-mw='{"parts":[{"template":{"target":{"wt":"#invoke:test","function":"invoke"},"params":{"1":{"wt":"blah"}},"i":0}}]}'><span class="scribunto-error" id="mw-scribunto-error-d64a22ba">Script error: The function <span typeof="mw:Entity">"</span>blah<span typeof="mw:Entity">"</span> does not exist.</span></strong></p>
+<p><strong class="error" about="#mwt1" typeof="mw:Transclusion" data-mw='{"parts":[{"template":{"target":{"wt":"#invoke:test","function":"invoke"},"params":{"1":{"wt":"blah"}},"i":0}}]}'><span class="scribunto-error mw-scribunto-error-d64a22ba">Script error: The function <span typeof="mw:Entity">"</span>blah<span typeof="mw:Entity">"</span> does not exist.</span></strong></p>
 !! end
 
 !! test