diff --git a/components/style/stylesheets/supports_rule.rs b/components/style/stylesheets/supports_rule.rs
index 2049bbce7ec..7d87f0f4aec 100644
--- a/components/style/stylesheets/supports_rule.rs
+++ b/components/style/stylesheets/supports_rule.rs
@@ -4,7 +4,7 @@
 
 //! [@supports rules](https://drafts.csswg.org/css-conditional-3/#at-supports)
 
-use cssparser::{parse_important, Parser, SourceLocation, Token};
+use cssparser::{Delimiter, parse_important, Parser, SourceLocation, Token};
 use parser::ParserContext;
 use properties::{PropertyId, PropertyDeclaration, SourcePropertyDeclaration};
 use shared_lock::{DeepCloneWithLock, Locked, SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
@@ -263,7 +263,10 @@ impl Declaration {
         let mut input = Parser::new(&self.val);
         let context = ParserContext::new_with_rule_type(cx, Some(CssRuleType::Style));
         let mut declarations = SourcePropertyDeclaration::new();
-        let res = PropertyDeclaration::parse_into(&mut declarations, id, &context, &mut input);
+        let res = input.parse_until_before(Delimiter::Bang, |input| {
+            PropertyDeclaration::parse_into(&mut declarations, id, &context, input)
+                .map_err(|_| ())
+        });
         let _ = input.try(parse_important);
         res.is_ok() && input.is_exhausted()
     }
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 6937d4fff10..9c32761a9fe 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -2298,7 +2298,7 @@ pub extern "C" fn Servo_CSSSupports2(property: *const nsACString,
 pub extern "C" fn Servo_CSSSupports(cond: *const nsACString) -> bool {
     let condition = unsafe { cond.as_ref().unwrap().as_str_unchecked() };
     let mut input = Parser::new(&condition);
-    let cond = parse_condition_or_declaration(&mut input);
+    let cond = input.parse_entirely(|i| parse_condition_or_declaration(i));
     if let Ok(cond) = cond {
         let url_data = unsafe { dummy_url_data() };
         let reporter = RustLogReporter;