diff --git a/components/style/gecko_bindings/nsstring_vendor/src/lib.rs b/components/style/gecko_bindings/nsstring_vendor/src/lib.rs
index 7080e57cbd0..af0ba1d1918 100644
--- a/components/style/gecko_bindings/nsstring_vendor/src/lib.rs
+++ b/components/style/gecko_bindings/nsstring_vendor/src/lib.rs
@@ -144,6 +144,7 @@ use std::ptr;
 use std::mem;
 use std::fmt;
 use std::cmp;
+use std::str;
 use std::u32;
 
 //////////////////////////////////
@@ -569,6 +570,10 @@ impl nsACString {
             Gecko_AppendUTF16toCString(self as *mut _, other as *const _);
         }
     }
+
+    pub unsafe fn as_str_unchecked(&self) -> &str {
+        str::from_utf8_unchecked(self)
+    }
 }
 
 impl<'a> From<&'a str> for nsCString<'a> {