diff --git a/lrlex/src/lib/parser.rs b/lrlex/src/lib/parser.rs
index 6d6d65c9b..9917314ba 100644
--- a/lrlex/src/lib/parser.rs
+++ b/lrlex/src/lib/parser.rs
@@ -1321,7 +1321,8 @@ a\[\]a 'aboxa'
         LRNonStreamingLexerDef::<DefaultLexeme<u8>, u8>::from_str(&src).ok();
     }
 
-    /// Test with various /// [Pattern_White_Space](https://unicode.org/reports/tr31/) separators.
+    /// Test that we accept various [Pattern_White_Space](https://unicode.org/reports/tr31/)
+    /// separators and reject other unicode whitespace separators.
     #[test]
     fn test_various_whitespace() {
         let src = "
@@ -1330,6 +1331,11 @@ a\[\]a 'aboxa'
         %%
         A	;
         B 'b'
C 'c'
D	'A'";
-        LRNonStreamingLexerDef::<DefaultLexeme<u8>, u8>::from_str(src).ok();
+        assert!(LRNonStreamingLexerDef::<DefaultLexeme<u8>, u8>::from_str(src).is_ok());
+        // En Space isn't part of Pattern_White_Space.
+        let src = "%S X Y";
+        LRNonStreamingLexerDef::<DefaultLexeme<u8>, u8>::from_str(src).expect_error_at_line_col(src, LexErrorKind::InvalidStartStateName, 1, 4);
+        let src = "%S X ";
+        LRNonStreamingLexerDef::<DefaultLexeme<u8>, u8>::from_str(src).expect_error_at_line_col(src, LexErrorKind::UnknownDeclaration, 1, 5);
     }
 }